Plating bath and surface treatment compositions for thin film deposition

ABSTRACT

An aqueous substrate surface treatment composition includes cysteine and an acidic solution having a pH of about 7 or less. The composition enables a selective deposition of a metal ion sensitizer and a subsequent selective plating of a metallic cap layer. Various CoWP plating bath compositions are also provided which may be used to form the cap layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application also claims priority to U.S. Provisional PatentApplication Ser. Nos. 60/680,491 filed on May 13, 2005, and 60/752,019filed on Dec. 12, 2005. Both applications are incorporated herein byreference in their entirety.

BACKGROUND

The invention is generally directed to plating bath and surfacetreatment compositions for forming thin films in electronic devices,such as semiconductor and other solid state devices.

Much research and design focus has been to scale electronic devices tovery small dimensions. However to ultimately take advantage of suchsmall scaling, higher performance interconnects are required. To date,aluminum has been the metal used to create such interconnects and buslines as in liquid crystal displays (LCDs). But with the scaling ofinterconnects, cross sectional area, line resistance and current densitycapacity are a limiting factor of total chip performance. Additionallyfor some applications like LCD bus lines, aluminum does not haveadequate conductivity as displays get larger. To overcome theselimitations, industry is moving away from Al towards use of copper,which has a resistivity of 1.72μ cm, approximately ⅔ of pure Al oralmost half of Al/0.5% Cu. Copper also has an increased current densitythreshold, which ultimately may make use of copper as interconnects morereliable and able to handle higher currents.

Copper, however, is not compatible with the subtractive etch processesthat are traditionally used in forming Al interconnects. Therefore, aprocess known as a dual damascene approach is used with both copper andaluminum, where a via is etched, followed or preceded by etching of atrench, allowing for creation of both trenches and vias in the samedielectric layer. Both structures are then filled with Cu, and then theresultant structure is polished using chemical mechanical polishing,resulting in an inlaid Cu interconnect.

However, the process of filling the trenches with copper is not a simplesingle step. Because copper readily migrates into the surroundingdielectric, such as SiO₂, barrier layers such as TaN are depositedbefore the addition of Cu. The Cu is then deposited on the barrier layerin a two step process, starting with a seed layer step followed by asubsequent enhancement step, either by electroplating or vapordeposition. This seed layer's characteristics play an important role inthe overall structure of the resultant film. A strongly textured seedlayer is important in forming an overall surface that is smooth and haslarge grains in the overall film. The texture, or orientationdistribution of polycrystalline materials, can affect the physicalproperties of the metal film, and as such, the (111) texture in copperfilms is generally preferred over (200) texture due to increasedelectromigration times. With the proper barrier and seed layers, thegrains of electroplated copper films in trenches are quite large and anear-bamboo structure can be obtained. This desirable microstructureenhances the reliability of damascene copper interconnects. Fine grainsizes often also degrade electromigration times, which typically occurwith chemical vapor deposition processes of the film rather thanelectroplating process.

Despite their advantages, there are difficulties in implementing copperinterconnects. For example, the copper interconnects are affected byelectromigration, i.e., movement of copper under an electric potentialgradient. Barrier layers in vias and trenches, underneath the copperlayer, have been used to prevent copper electromigration and can also beused to improve copper adhesion to the dielectric material. Morerecently, a barrier layer deposited on top of the copper filled trench,referred to as a cap layer, is used to prevent copper migration at theinterface between the top of the copper layer in a trench and the nextdielectric layer. See Hu et al., RELIABILITY PHYSICS SYMPOSIUMPROCEEDINGS, 42^(nd) Annual (2004 IEEE International); Kohn et al.,JOURNAL OF APPLIED PHYSICS 92(9):5508-5511 (2002). One approach toforming this capping layer is to deposit a thin layer of the appropriatecap material on the entire wafer followed by a patterning step to removethe cap material from the dielectric surface. Electroless plating hasalso been used to form cap layers.

Today, there is no cost effective means of depositing a lower resistancemetal such as copper. In the semiconductor interconnect application,seed layers are created by atomic layer deposition which is expensiveand has inadequate coverage of high aspect ratio vias.

In addition, there is currently no cost effective means of forming a caplayer using a deposition and patterning technique, and the use ofelectroless plating suffers from a number of shortcomings. For example,limited selectivity and instability of the electroless deposition bathmake the use of electroless plating for forming cap layers less thanideal.

SUMMARY

An embodiment of the invention provides an aqueous substrate surfacetreatment composition which comprises cysteine and an acidic solutionhaving a pH of about 7 or less. The composition enables a selectivedeposition of a metal ion sensitizer and a subsequent selective platingof a metallic cap layer. Other embodiments of the invention provide CoWPplating bath compositions which may be used to form the cap layer.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a TEM image of Au nanoparticles created by reduction of Ausalt with NaBH₄ and subsequent ultra-filtration. FIG. 1B is a plot of Auparticle diameter distribution.

FIG. 2 is a schematic of an Au nanoparticle stabilized by CALNN (SEQ IDNO: 1) peptide.

FIG. 3 shows AFM images of a biologically directed Au seed layer,followed by electroless plating (EP) enhancement. The left image showsthe seed layer, the middle image shows the film after the first EP stepand the right image shows the film after a second EP step.

FIG. 4 is an AFM analysis of grain size of the metal film after thefirst (left image) versus the second (right image) EP step.

FIG. 5 is a 10× image of PDMS printed biological seed layer.

FIG. 6 shows images of peptide-gold nanoparticle seed layer pattern thatwas further enhanced by Au electroplating.

FIG. 7 shows AFM images of the EP Au film pattern.

FIG. 8 shows an image of structure made by providing a peptide 2-Aunanoparticle seed layer microcontact printed onto a 1737 glass substrateand annealed, followed by forming a patterned copper film by EP.

FIG. 9 shows images of CALNN (SEQ ID NO: 1) Pd nanoparticles from pH 13solution on Streptavidin coated glass for 10 and 3 minute growth timesat 40 C (left and center images, respectively) and of a control samplewhich lacked Pd nanoparticles (right image).

FIG. 10 shows images of CALNN (SEQ ID NO: 1) Pd nanoparticles from pH 9solution with growth at 40° C. and 53° C. on Streptavidin andpoly-lysine coated glass, respectively.

FIG. 11 shows images of CALNN (SEQ ID NO: 1) Pd nanoparticles from pH 9Solution with twenty minutes growth at 53° C. on poly-lysine coatedglass.

FIG. 12 shows AFM images of Au-Peptide 2 nanoparticle seed layers on1737 glass.

FIG. 13 shows images of growth of thin copper films on Corning 1737glass using Au nanoparticle seed layers formed using peptide 2.

FIG. 14 shows AFM measurements of copper films on Corning 1737 glass.

FIG. 15 shows additional copper films formed by using a goldnanoparticle seed layer. The seed layer solution was purified byultra-filtration.

FIG. 16 shows Cu film growth on a tantalum nitride substrate using Aunanoparticles as a seed layer.

FIG. 17 is an AFM analysis of Cu film growth on tantalum nitride usingthe Au nanoparticle seed layer.

FIGS. 18A-18I, 19A-19I, 20A-20D, 21 and 22 show schematic side crosssectional views of steps of alternative methods of making a deviceaccording to the embodiments of the invention.

FIGS. 23-28G illustrate various aspects of the eighth example of theinvention.

FIGS. 29-31 b illustrate various aspects of the ninth example of theinvention.

FIG. 32 illustrates various aspects of the tenth example of theinvention.

FIG. 33 illustrates various aspects of the eleventh example of theinvention.

DETAILED DESCRIPTION Introduction

All references cited herein are incorporated by reference in theirentirety. No admission is made that any of these references are priorart.

The embodiments of the present invention provide a method of forming aseed layer on a substrate using a biological agent. The seed layer maycomprise densified nanoparticles or metal ions which are bound to thebiological agent. The seed layer is then used for a deposition of ametal layer. For example, the metal layer may comprise a barrier layer,an interconnect layer, a cap layer for the interconnect layer or a busline layer.

In the first five sections below, the biological agent, the substrate,suitable patterning methods, the seed layer and the enhancement layerare described in more detail. Then, in the subsequent three sections, amethod of making a metal structure according to the first, the secondand the third embodiments, respectively, are described. Then, theworking examples are described.

Biological Agent

Any suitable biological agents, such as peptides, viruses, proteins,amino acids, nucleic acids, or lipids that possess a functionalitydescribed below may be used. The preferred biological agent is peptide,which may have an engineered functionality, and a wide variety ofpeptide structures comprising linked amino acids can be used. Thecomposition comprising the peptide may also optionally comprise a liquiddispersion medium for the peptide and the seed layer nanoparticles, aswill be described in more detail in the subsequent sections. Thecomponents for the liquid dispersion medium are not particularly limitedand mixtures of components can be used. Water-based or organic-basedcomponents can be used. Examples include water, fluorocarbons,n-alkanes, alcohols, acetonitrile, methanol, ethanol, propanol,isopropanol, hexanes, dodecane, toluene, cyclohexanone, diethyl ether,tetrahydrofuran, dichloromethane, and acetone. Mixtures can be usedincluding mixing in small amounts of organic solvent in water. Theliquids should be able to volatilize as needed for the particularapplication. Factors to consider in solvent selection further includehydrophilicity of the substrate surface, solubility of thenanoparticles, vapor pressure, toxicity, purity, and the like.Surfactants, binders, dispersion agents, and other coating additives canbe used as needed. Buffers can be used to control the pH. For example,the pH can be 7 or below, or 7 or above. The pH can be 7-10, 7-9, or7-8. Stable colloid solutions can be formed and purified further asneeded. For example, purification by gel filtration or ultrafiltrationcan be carried out. Other purification methods include filtration usinga Nanosep 10K centrifugal filter.

The concentrations of the peptide and the nanoparticles can becontrolled for particular applications. Concentrations can be, forexample, 1 M or less, 0.5 M or less, 0.1 M or less, 0.05 M or less, 0.01M or less, or 0.005 M or less (e.g., 5 mM or less). Concentration can beadjusted to provide the best balance of nanoparticle density in the seedlayer and the quality of formation of nanoparticles when nanoparticlesare formed in the presence of peptide. Reaction conditions can be variedto adjust the shape and size of nanoparticles, and concentration is onesuch reaction condition, along with temperature. In general, thenanoparticles can be well dispersed in the dispersion medium and can bestably dispersed over time.

A wide variety of peptides can be used of various molecular weights asthe biological agent. The peptides can be natural peptides, nonnaturalpeptides, unnatural peptides, synthetic peptides, or peptide analogs.Peptides may also be found in nature, or modified from those found innature, and the study of nature can be used to determine useful peptidesequences. Phage display and other combinatorial or library methods canbe used to determine suitable peptides. The peptides can beoligopeptides or polypeptides. A wide variety of amino acids can be usedincluding those found in nature. The peptide can comprise a firstpeptide binding domain for binding to the nanoparticle. The peptide canfurther comprise a second binding domain for binding to the substrate.

The peptide can be a low molecular weight peptide (e.g., 100 amino acidunits or less, or 50 amino acid units or less, or about 10 to about 30amino acids) or can be part of a larger protein or support complex. Thepeptide can be a bifunctional peptide. The two active peptide bindingdomains can be directly linked to each other or can be linked to eachother through an intermediate spacer unit. The intermediate spacer unititself can be a peptide linkage. The peptide can be represented by thesymbol A-B-C, wherein A is a first binding peptide moiety for binding tothe seed layer nanoparticles (or metal ions if the ions are used insteadof nanoparticles), B is an optional intermediate non-binder linker, andC is a second binding peptide moiety for binding to a surface. Forexample, B may be a protein scaffold, such as Thioredoxin, as will bedescribed below. When B is not present, the symbol collapses to A-C.Alternatively, a single amino acid or fusion protein may be used insteadof the peptide as the biological agent. If a single amino acid is used,then the amino acid may be a bifunctional amino acid, such as cysteine.The protein may comprise a bifunctional protein comprising a scaffoldconnecting substrate and seed layer specific binding regions.

The peptides can be also used in the synthesis of nanoparticles, wherethey can act as capping ligands to control nanoparticle shape, size, andcrystal morphology. Peptides can also passivate the nanoparticle,improving long term stability. Peptides can be localized onto thesubstrate surface via affinity, streptavidin/biotin interaction, orthrough direct adsorption/placement.

Additionally, commercially available nanoparticles can be used as a seedlayer. These commercial nanoparticles come with ligands encapsulatingthem. At times, these nanoparticles can be used with the ligands assupplied, for example, with linkages such as streptavidin or biotin, orwith counter ions. Primarily, commercial nanoparticles can be used wherethe nanoparticles are stabilized by counter ions, such as acetate.Because these counter ion stabilized nanoparticles are typically notstable when salt is added to a solution containing them, ligand exchangecan be performed, where a peptide of interest is exchanged with theoriginal counter ion to functionalize the nanoparticles with moleculesthat make them stable in salt solutions/change their solubility, and/orcan act as a hook to cause directed placement for immobilization on thesurface.

Specific biological complexes or binding pairs known in the art such as,for example, biotin and streptavidin can be used to promote bondingbetween the peptide and the surface. Other examples includeglutathione-S-transferase/glutathione; 6× Histidine Tag/Ni-NTA;S-protein/S-peptide; or biotin/avidin. Peptides can be, for example,biotinylated and can be synthesized through commercial peptide synthesisvendors. For example, peptide 3222, with a sequence of CALNN (SEQ ID NO:1), a known covalent Au binder found in the literature (Levy et al., J.Amer. Chem. Soc., 126, No. 32, pp. 10076-10084, 2004, which is hereinincorporated by reference in its entirety), was made synthetically(Peptide 3222A) as well as synthesized with a biotin added on the Nterminus (Peptide 3222B). This peptide can be designed to stabilize Aunanoparticles by forming a dense, self-assembled monolayer (FIG. 2).Stabilized nanoparticles produced using this peptide can be purified andhandled like stable proteins (e.g., by size exclusion chromatography,ultrafiltration, electrophoresis, lyophilization, and the like).

Au nanoparticles can be prepared with this peptide either by reductionof a precursor or by ligand exchange. A biotinylated version of thatpeptide was prepared and found to also give stable Au colloids.

Thus, in general, any suitable metal and other nanoparticles may be usedwith the peptides. The nanoparticles may comprise pre-made nanoparticleswhich are subsequently bound to the peptides. Alternatively, thenanoparticles may be nucleated and grown on the peptides from a metalcontaining solution. For example, metal nanoparticles may be nucleatedfrom a metal ion containing solution by using a reducing agent, such asNaBH₄ or dimethylamine borane. The metal nanoparticles may also benucleated without a reducing agent when the peptide contains a reducingcomponent. For example, a peptide may comprise a cysteine componentwhich contains a free thiol group that assists in nucleation of a metalnanoparticle from a metal salt solution.

The peptide itself or the peptide's other binding site such as, forexample, the peptide's biotin functionality can be exploited forspecific localization onto a surface or a substrate. Alternatively, thepeptide can be directly adsorbed to a surface or substrate or can beinteracted with the substrate in a patterned way, so that the subsequentfilms grown follow the shape of the peptide pattern. Also, bifunctionalpeptides can be used, where one end of the peptide or virus isengineered to bind to a seed material, while the other end of thepeptide has engineered specificity to bind to a substrate or surface.

Generally, non-covalent binding is desired between the peptide and thenanoparticle, and between the peptide and the substrate surface.However, covalent bonding may also be used in some circumstances. Forexample, if an amino acid instead of a peptide is used, then the aminoacid may be covalently bonded to the substrate and/or to thenanoparticle. Furthermore, peptide covalent bonding may also be used,such as peptides that have cysteine at one end that could participate incovalent binding via the thiol. Also, cyclic peptides that areconstrained by a disulfide bond could be exposed to reducing conditionwhich would open the ring and allow the freed thiols to participate incovalent binding to metals.

Other peptides include phage display discovered peptides screenedagainst Au (Peptide 1: VSGSSPDS (SEQ ID NO: 2); Peptide 2: LKAHLPPSRLP(SEQ ID NO: 3)) as well as peptides obtained from the literature thatare known to interact with Au (Peptide 3: MHGKTQATSGTIQS (SEQ ID NO: 4),see for example Brown, S., “Metal Recognition by RepeatingPolypeptides,” Nature Biotechnol., 15, 269-272 (1997), which is herebyincorporated by reference in its entirety). Peptides can be synthesizedwith biotin on their N-termini and HPLC purified to >90% purity.Peptides can also be synthesized with biotin on their C-termini throughan additional Lys (Lysine) or Ser (Seine). If desired, purification canbe carried out so that purity is, for example, greater than 95%, orgreater than 99%. However, it is possible that a purity below 90% mayalso be sufficient. These Au peptides can also be used to grow othernanoparticles, including Pd nanoparticles, in addition to Aunanoparticles. Some peptides can have a high affinity for multiplematerials. For example, peptide 2, in addition to being able to bind toor grow gold, also has a high affinity for glass, plastic, oxide andnitride surfaces, such as Corning 1737 glass, soda lime glass, Kapton®,SiO₂, TiO₂ and tantalum nitride, for example. Peptides with multipleaffinities, therefore, can be used.

In addition, one skilled in the art, if needed, can refer to thefollowing patent literature for selection of binding peptides usingvirus, genetic engineering methods, and for materials to be used withgenetically engineered viruses. Phage display, yeast display or cellsurface display systems can be used for panning peptides. Phage displaylibraries and experimental methods for using them in biopanning arefurther described, for example, in the following U.S. patentpublications to Belcher et al.: (1) “Biological Control of NanoparticleNucleation, Shape, and Crystal Phase”; 2003/0068900 published Apr. 10,2003; (2) “Nanoscale Ordering of Hybrid Materials Using GeneticallyEngineered Mesoscale Virus”; 2003/0073104 published Apr. 17, 2003; (3)“Biological Control of Nanoparticles”; 2003/0113714 published Jun. 19,2003; and (4) “Molecular Recognition of Materials”; 2003/0148380published Aug. 7, 2003, which are each hereby incorporated by referencein their entirety. Additional patent applications useful for one skilledin the art describe viral and peptide recognition studies with use ofgenetically engineered viruses for materials synthesis and applicationsincluding, for example, (1) U.S. Ser. No. 10/654,623 filed Sep. 4, 2003to Belcher et al. (“Compositions, Methods, and Use of Bi-FunctionalBioMaterials”), published 2004/0127640; (2) U.S. Ser. No. 10/665,721filed Sep. 22, 2003 to Belcher et al. (“Peptide Mediated Synthesis ofMetallic and Magnetic Materials”), published 2005/0064508; (3) U.S. Ser.No. 10/668,600 filed Sep. 24, 2003 to Belcher et al. (“FabricatedBioFilm Storage Device”), published 2004/0171139; (4) U.S. Ser. No.10/965,665, filed Oct. 15, 2004 to Belcher et al. (“Viral Fibers”); (5)U.S. Ser. No. 10/965,227 filed Oct. 15, 2004 to Belcher et al.(“Multifunctional Biomaterials . . . ”); and (6) U.S. Ser. No.10/976,179, filed Oct. 29, 2004 to Belcher et al. (“InorganicNanowires”) each of which is hereby incorporated by reference. Thesereferences describe a variety of specific binding modifications whichcan be carried out for binding to conjugate structures, as well asforming the conjugate structures in the presence of the materialmodified for specific binding. Semiconductor applications ofbifunctional peptides are described in, for example, U.S. provisionalapplication 60/571,532 filed May 17, 2004, which is hereby incorporatedby reference in its entirety. Yeast display peptide systems aredescribed in, for example, U.S. application Ser. No. 11/051,481 filedFeb. 7, 2005, which is hereby incorporated by reference in its entirety.

Reiss et al., “Biological Routes to Metal Alloy FerromagneticNanostructures,” Nanoletters, 2004, Vol. 4, No. 6, 1127-1132 describespeptides for binding to metals, including mediating nanoparticlesynthesis, and is hereby incorporated by reference in its entirety.Flynn, Mao, et al., “Synthesis and Organization of Nanoscale II-VIsemiconductor materials using evolved peptide specificity and viralcapsid assembly,” J. Mater. Sci., 2003, 13, 2414-2421, describespeptides for binding to and nucleation of semiconductor nanoparticles,and is hereby incorporated by reference in its entirety. Mao, Flynn etal., “Viral Assembly of Oriented Quantum Dot Nanowires,” PNAS, Jun. 10,2003, vol. 100, no. 12, 6946-6951 further describes peptides for bindingto and nucleation of semiconductor nanoparticles, and is herebyincorporated by reference in its entirety.

The biological materials, and in particular the peptides, once placementof a seed layer is successfully completed, can be generally volatilizedand removed so that, preferably, they cannot be detected in the finalfilm. However, some residue may remain in a final product reflecting thesource of the intermediate product comprising the peptides. Thissubstantial removal can be described in terms of weight percentageremaining. For example, the amount of remaining biological materialswith respect to the total amount of film including biologicals can beless than 1 wt. %, more preferably, less than 0.5 wt. %, and morepreferably, less than 0.1 wt. %. Embodiments include both intermediateproducts which comprise the peptides and final products which compriseonly peptide residue or substantially no peptide or peptide residue.Residues can be analyzed by, for example, carbon content includingsurface analysis such as XPS. In other patent applications, which arehereby incorporated by reference in its entirety, [U.S. Ser. No.10/665,721 filed Sep. 22, 2003 to Belcher et al. (“Peptide MediatedSynthesis of Metallic and Magnetic Materials”), published 2005/0064508;and U.S. application Ser. No. 10/976,179, filed Oct. 29, 2004 to Belcheret al. (“Inorganic Nanowires”)], (see also Mao et al., Science, vol.303, Jan. 9, 2004, pages 213-217) additional description is provided forburning off and elimination of biologicals from materials to which thebiologicals can selectively bind. For example, annealing temperatures of500-1,000° C. are described for burning off the biologicals or peptides.Sintering methods can be used.

Heating to remove the peptide can also result in effects on thenanoparticle seed layer. For example, nanoparticles can coalesce withheating and form a more continuous or “fused” film. Heating can alsoenhance the film's adherence to the substrate.

Substrate

As used herein, the term “substrate” means any structure containing oneor more layers upon which the biological agent is deposited. The term“supporting substrate” means the supporting member, such as asemiconductor wafer or a glass plate, upon which a solid state device isfabricated. Thus, a “substrate” may comprise either a bare “supportingsubstrate” or a “supporting substrate” covered by one or more layersand/or devices.

A variety of materials can be used for the substrate, presenting asurface for deposition of the seed layer, as will be described in moredetail below. The substrate may include electrically conductive,semiconducting, or insulating materials. The substrate can include amultilayer substrate. The substrate can be, for example, insulatingmaterials such as a low-k polymer dielectric, glass, quartz, oxide ornitride material, plastic or ceramic; semiconductor materials such assilicon, germanium, gallium arsenide and the like; and conductivematerials such as metals, including aluminum, copper, stainless steeland the like; as well as composites of materials including metals andsemiconductors, and multilayer coating of any of these materials.

The substrate typically comprises a surface where a metal film, such asa copper film, would be grown. Such substrates include, for example,barrier layer materials, such as Ta, TaN, Ti, TiN, TiW, Mo and/or Cr,and insulating materials, such as silicon oxide (including silicondioxide), silicon nitride, and silicon oxynitride. Thus, the barrierlayer materials comprise blocking materials which prevent copperdiffusion. The substrate may also comprise a metal interconnect, such asa copper, nickel, or other conductive interconnect metal on which a caplayer is grown, as will be described in more detail below. Thesubstrates may be cleaned, prepared, or coated with a oxide or othersubstance.

The substrate may be coated with streptavidin so that the affinitybetween the peptide and the substrate is a stable streptavidin-biotininteraction. Other substrate coatings to exploit for directed biologicalplacement include poly-Lysine surfaces. Silane surface may also be used.The peptide may also be directly bound to the substrate without anycoating on the substrate in order to direct the metal film directly onthe desired layer.

The substrate can be a substrate useful for fabrication of semiconductoror other solid state electronic devices, such as transistor containinglogic or memory devices. The substrate can comprise features used insmall-scale semiconductor processing including damascene features. Forexample, the substrate can comprise trenches and/or vias with highaspect ratios including, for example, aspect ratios of 2 or greater, 4or greater, 6 or greater, 8 or greater, or 10 or greater. The width canbe, for example, 200 nm or greater, 400 nm or greater, 600 nm orgreater, 800 nm or greater, or one micron or greater. The depth can be,for example, 600 nm or greater, 800 nm or greater, one micron orgreater, two microns or greater, three microns or greater. Particularadvantages can be gained when substrates are used which have featureswhich are difficult to conformally coat such as high aspect ratiofeatures. In general, the substrate can be a non-particulate substrateand presents non-particulate surfaces to the seed layer.

Substrates also can be selected for usefulness in displays includingliquid crystal displays, plasma displays, LED displays and organic LEDdisplays. Deposition of seed layers on glass substrates is described inU.S. Pat. No. 6,887,776, which is hereby incorporated by reference inits entirety. Glasses include undoped silica glass (USG), phosphorousdoped glass (PSG), boron-phosphorous doped glass (BPSG), soda-limeglass, borosilicate glass, sodium borosilicate glass, alkali-metalborosilicate, aluminosilicate glass, aluminoborosilicate glass, alkalineearth aluminoborosilicate glass, alkaline earth-metalaluminoborosilicate glass, and combinations thereof.

Patterning

As will be described with respect to the methods of the first, secondand third embodiments in the sections below, certain layers or materialsare patterned. Any suitable patterning method may be used.

For example, photolithography may be used to pattern a layer by forminga resist or another radiation sensitive material over the layer andselectively exposing the resist to an energy beam. For example,photosensitive resists may be exposed to a UV or visible light beamthrough a mask. Electron beam sensitive resists may be exposed to ascanned electron beam. Then, either the exposed or non-exposed regionsof the resist (depending if a positive or a negative resist is used) areremoved. The remaining regions of the resist are then used as a mask forwet and/or dry etching of the underlying layer to pattern the underlyinglayer.

Alternatively, the patterning may comprise forming the layer over orthrough a mask. For example, the layer may be deposited through openingsin a mask to form a layer pattern. Alternatively, the layer may beformed on a resist pattern. The resist pattern is then lifted-off toform the layer pattern by the lift-off method. Screen printing,flexoprinting, gravure printing, microcontact printing and ink jetprinting or patterning can also be used to form layer patterns.

For example, metal lines can be patterned having line width of 250microns or less, 100 microns or less, 10 microns or less, one micron orless, 500 microns or less, or 100 nm or less. The distances betweenpatterned features can be, for example, 10 microns or less, one micronor less, or 500 nm or less. High resolution patterning is generallypreferred. Optical or electron microscopy or scanning probe methods canbe used to characterize the pattern.

General methods for patterning, lithography, and direct-write are knownin the art as described in for example, (i) Pique (Ed.), Direct-WriteTechnologies for Rapid Prototyping Applications, 2002, Academic Press,including Chapter 18, and (ii) Madou, Fundamentals of Microfabrication,The Science of Miniaturization, 2^(nd) Ed., CRC Press, 2002, pages344-357, which are hereby incorporated by reference in their entirety.

Nanoparticles/Seed Layer

A seed layer can be disposed on the substrate. The seed layer provides acatalytic effect when later a metal, such as a copper interconnect, isfurther disposed on the seed layer. The seed layer may also influencethe texture of a metal, such as copper, which is further disposed on theseed layer. For example, copper <111> texture can be enhanced to providebetter electromigration performance, and higher orientation can beachieved. The seed layer step coverage, conformality, and texture can beadapted for particular applications.

The seed layer material may be selected to allow a selective metaldeposition step, such as a copper interconnect deposition step, abarrier layer deposition step and/or a cap layer deposition step. Forexample, the seed layer material is selected to catalyze selectivecopper deposition from a copper solution (i.e., copper plating) on theseed layer. This metal deposition step is referred to herein as an“enhancement step” to form a continuous “enhancement” layer or film.

In the case of Cu enhancement, Au, Pd, Ru and Ni seed layers have beenshown in the literature to form Cu films after electro/electroless Cuplating. Many other metals can be used as a seed layer that catalyzecopper plating (see Chapter 12 “Fundamentals of Electroless CopperPlating”, Bindra & White). Other examples include aluminum, silver,manganese, molybdenum, platinum, tin, zinc, tantalum, titanium, alloys,oxides, nitrides, and phosphides thereof.

The seed layer can comprise material, such as metal, which is the samematerial as the enhancement layer, or different material from theenhancement layer. For example, gold seed layers can be used for bothgold and copper enhancement layers.

The seed layer material may have any suitable form, such as metal ionsor nanoparticles. The nanoparticles do not generally require thepresence of a surface coating to allow binding to the biological agentsuch as the peptide. Nanoparticles can be inorganic nanoparticles ormetallic nanoparticles including alloys. In some embodiments, they canbe semiconductor nanoparticles. Nanoparticles can be quantum dots.Examples of semiconductor nanoparticles include cadmium sulfide, cadmiumselenide, silver sulfide, cadmium sulfide, zinc sulfide, zinc selenide,lead sulfide, gallium arsenide, silicon, tin oxide, iron oxide, andindium phosphide. Nanoparticles can be crystalline or amorphous. Thenanoparticles also can be nanocrystals. The nanoparticles can beamorphous or crystalline, and if crystalline can show differentcrystalline phases. For copper interconnect deposition, thenanoparticles preferably comprise nanoparticles of a material, such asCu, Au, Ru, Ni, Ag, Pt, Co, Pd, etc., which catalyze selective copperplating.

The nanoparticles can be characterized by particle sizes which can be,for example, about 100 nm or less, about 50 nm or less, about 25 nm orless, or about 10 nm or less. The particle size can be, for example,about 1 nm or more, or about 3 nm or more, or about 5 nm or more. Theparticle size can be, for example, about 1 nm to about 10 nm. Theparticle size can be determined by a linear dimension in any directionon the order of nanometers, e.g., 1 nm to 100 nm. Particle sizedistribution can be for example less than 30% of the average particlediameter for nanoparticles having an average diameter of 10 nm or less.The size of the nanoparticle can affect the melting temperature of thematerial, and the skilled artisan can adjust this parameter to achieve adesired melting performance for a specific application. If desired, thenanoparticles can be polydisperse or substantially monodisperse in size.For example, the particle size can have a standard deviation of 5% orless. Nanoparticles are not limited by a particular aspect ratio butgenerally will not be nanowires and generally can have aspect ratios ofabout 10:1 or less. Dimensions can be sufficiently small to provide forquantum confinement effects. Core-shell structures can also be used.

Solution phase reduction from a metal salt can be used to prepare thenanoparticles. Alternatively, nanoparticles can be prefabricated byother methods, without use of the biological agent such as peptide, andthen bound to the biological agent such as peptide.

Growth of nanoparticles in the presence of biological agents, such aspeptides is described in the aforementioned Belcher patent publicationsand technical literature including, for example:

Reiss et al., “Biological Routes to Metal Alloy FerromagneticNanostructures,” Nanoletters, 2004, Vol. 4, No. 6, 1127-1132 describespeptides for binding to metals, including mediating nanoparticlesynthesis, and is hereby incorporated by reference in its entirety.

Flynn, Mao, et al., “Synthesis and Organization of Nanoscale II-VIsemiconductor materials using evolved peptide specificity and viralcapsid assembly,” J. Mater. Sci., 2003, 13, 2414-2421, describespeptides for binding to and nucleation of semiconductor nanoparticles,and is hereby incorporated by reference in its entirety.

Mao, Flynn et al., “Viral Assembly of Oriented Quantum Dot Nanowires,”PNAS, Jun. 10, 2003, vol. 100, no. 12, 6946-6951 further describespeptides for binding to and nucleation of semiconductor nanoparticles,and is hereby incorporated by reference in its entirety.

The following patents are incorporated by reference in their entirety:U.S. Pat. No. 6,207,392 to Weiss et al. describe semiconductornanocrystals and linking agents; U.S. Pat. No. 6,235,540 describessemiconductor nanoparticles linked to ligands; and U.S. Pat. No.6,417,340 describes nanoparticles.

Naik et al., Nature Materials, vol. 1, Nov. 2002, 169-172 furtherdescribes synthesis and patterning of silver nanoparticles; and Naik etal., J. Nanosci. Nanotech. 2002, vol. 2, No. 1, pages 95-100.

An example of copper nanocrystal growth on peptides can be found inBanerjee et. al, PNAS, Dec. 9, 2003, 14678-14682, vol. 100, no. 25,which is hereby incorporated by reference in its entirety. Coppernanocrystals and seed layers are further described in U.S. Pat. No.6,887,297 and US Patent Publication 2004/0091625 (Winter) as well as inU.S. Pat. Nos. 6,780,765; 6,774,036; and 6,277,740 (Goldstein), whichare hereby incorporated by reference in their entirety.

The seed layer can be characterized by a coverage percentage. Forexample, coverage percentage can be 20% or greater, 40% or greater, 60%or greater, or 80% or greater. When the seed layer is disposed in atrench or via, the coverage can comprise both a coverage of the bottomand the coverage of the side wall. The coverage of the side wall can behigher than the coverage of the bottom. For example, the coverage of theside wall can be 40%, whereas the coverage of the bottom can be only20%. The coverage can be affected by the concentration of thenanoparticles in the solution, and this concentration can be varied tofacilitate control over the seed layer coverage and film thickness.

The seed layer can be also characterized by a film thickness. Forexample, film thickness can be for example 500 nm or less, or 250 nm orless, or 100 nm or less, such as 50 nm to 500 nm, or 50 nm to 250 nm, or100 nm to 250 nm. U.S. Pat. No. 6,879,051 describes one method todetermine seed layer thickness of trench side walls.

Technical literature related to seed layers include:

Biberger et al., http://www.novellus.com/damascus/tec/tec_(—)0.5.asp,“Low Pressure Sputtering of Copper, and Related Barriers, for SeedLayers and Complete Planarization.”

Healey, “Current Technical Trends: Dual Damascene & Low-k Dielectrics”;

Ryu et al, “Electromigration of Submicron Damascene CopperInterconnects” (1988 Symposium on VLSI Technology, Jun. 8-11, 1998);

Wong et al., “Barrier/Seed Layer Requirements for Copper Interconnects”1998 International Interconnect Technology Conference (San Francisco,Calif.), Jun. 3, 1998; and

Marasimhan et al., “InLine Process Control of Advanced Thin Films at 65nm and Beyond”, Summer 2004, Yield Management Solutions,www.kla-tencore.com/magazine, pages 1-16.

The seed layer can be formed on the substrate by a variety of liquiddeposition methods, including for example dip coating, spray coating,spin coating, and electrochemical deposition. Other deposition orpatterning techniques for the seed layer include printing (inkjet,offset, contact, and the like), electrophoretic deposition, slotcoating, drum coating, various ways of patterning molecules to capturethe nanoparticle seed, and the like. Microcontact printing can also beused to place the seed layer in desired locations on the substrate. Thepeptides may be placed on a microcontact stamp and then stamped orprinted onto desired portions of the substrate. As solvent evaporates,nanoparticles are selectively bound to the substrate by the biologicalagent. Specifically, the biological agent, such as a peptide, bound tothe nanoparticles, has a specific binding affinity for a particularsubstrate material.

If desired, seed layer can be uniformly applied to the entire substrate.If desired, the seed layer may be patterned to remain only over selectedsubstrate locations using photolithography or any other patterningmethod described above in the patterning section. A mask on thesubstrate can also be used to prevent deposition of the seed layer ontop of the substrate areas covered by the mask and to allow depositionof the seed layer on the unmasked regions.

For example, the seed layer may be selectively deposited in a via and/ortrench located in an interlayer insulating layer over a solid statedevice. Alternatively, the seed layer may be deposited over the entireinterlayer insulating layer and then patterned to remain in the viaand/or trench in the interlayer insulating layer. This allows asubsequent deposition of a barrier layer and/or a copper interconnect inthe via and/or trench, as will be described in more detail below andwith respect to the first and second embodiments.

If desired, the seed layer can be annealed with heat to increase densityand improve subsequent enhancement steps. For example, annealing can becarried out for at least 5 minutes, at least 10 minutes, or at least 20minutes. Annealing temperature can be for example at least 100° C., atleast 150° C., or at least 200° C. AFM imaging can be carried out beforeand after annealing and surface area roughness measured. Surface arearoughness before and after annealing can be for example 10 nm or less,or 5 nm or less, or 3 nm or less. Annealing can result in a reduction ofsurface area roughness of 5% to 30%, or 10% to 20%.

In many cases, conformal coatings of the seed layer are desired, andpeptide binding and conditions are selected to achieve conformalcoating. In many other cases, a selective deposition is desired whereinseed layer is formed in some areas but not others.

Enhancement Layer

After the seed layer is formed on the substrate, a metal layer (i.e.,the “enhancement” layer) is selectively deposited on the seed layer, aswill be described in more detail below. For example, the seed layer maybe located in a via and/or in a trench and the metal film may comprise abarrier layer and/or an interconnect which is selectively deposited inthe via and/or trench.

Thus, enhancement steps can be performed on the seed layers so that ametallic film is formed over the seed layer. These enhancementtechniques include electro plating and electroless plating. Additionalenhancement steps can be, for example, CVD or PVD/Fill. The enhancementstep can be repeated until the desired amount of enhancement isachieved. The films can be characterized by scanning probe methods,including AFM, and optical microscopy. The nature of the enhancement canbe measured with use of average grain size, linear dimensions, and grainsize standard deviations. For example, a first enhancement step can becarried out and a first average grain size measured; then a secondenhancement step can be carried out and a second average grain sizemeasured; and so forth. Average grain sizes can be for example 2,500 nm²or less, or 1,500 nm² or less.

If desired, the metal of the seed layer can be the same as the metal ofthe enhancement step, or they can be different metals. For example, theseed layer can be copper, but is not necessarily copper, when copper isused in the enhancement step.

Film thickness of the enhanced film can be, for example, one micron orless, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, or100 nm or less. Exemplary ranges include 50 nm to 500 nm, or 100 nm to200 nm. For the enhancement layer, surface area roughness before andafter annealing can be for example 10 nm or less, or 5 nm or less, or 3nm or less. Annealing can result in a reduction of surface arearoughness of 5% to 30%, or 10% to 20%.

The temperature of the enhancement step can be for example 100° C. orless, 80° C. or less, 60° C. or less, or 40° C. or less. Enhancementgrowth can be carried out with each step of for example one minute to300 minutes, or two minutes to 100 minutes. Temperature and time can beadjusted as needed for a particular application.

The final film, including final copper films, can be tested forresistivity. Resistivity can be, for example, 100 μΩ-cm or less, 50μΩ-cm or less, 10 μΩ-cm or less, or 1 μΩ-cm or less. Resistivity can be,for example, about 0.01 μΩ-cm or more, or about 0.1 μΩ-cm or more. Ingeneral, resistivity should be similar to bulk copper which is 1.7μΩ-cm. Resistivity range can be, for example, about 1.5 to about 4, orabout 1.7 to about 2.6 μΩ-cm.

Metal deposition processes, including electroless metal deposition,electrodeposition, and seed layers, are described in Madou, Fundamentalsof Microfabrication, The Science of Miniaturization, 2^(nd) Ed., CRCPress, 2002, pages 344-357, which is hereby incorporated by reference inits entirety. Copper deposition is particularly described. Electrolessdeposition is described in, for example, U.S. Pat. Nos. 5,891,513 and5,830,805, which are hereby incorporated by reference in their entirety.Furthermore, copper electroless plating compositions and methods areknown. For example, formaldehyde-based EP copper bath can be used.Another example is amine borane reducing agents and ligands based onneutral tetradentate nitrogen donors. See, for example R. Jagannathan etal., IBM J. Res. Develop., Vol. 37, No. 2, March 1993, pages 117-123,which is incorporated herein by reference in its entirety. An example ofelectroless gold deposition is Kato et al., J. Electrochem. Soc., 149,C164 (2002), which is hereby incorporated by reference in its entirety.Another example of electroless deposition of thin metallic films isPinto et al., Polymer Preprints, 2003, 44(2), 138-139, which is herebyincorporated by reference in its entirety. Electroless plating of goldand gold alloys is described in Okinaka, Chapter 15, “ElectrolessPlating of Gold and Gold Alloys, pages 401-420 (from ElectrolessPlating—Fundamentals and Applications, Ed. Mallory, Glenn O.; Hajdu,June B, 1990, William Andrew), which is hereby incorporated by referencein its entirety.

The process can further comprise the step of planarizing the metal layerlocated in a trench to produce a planarized metal layer in the trench,such that the top surface of the metal layer and the top of the trenchare co-planar. The planarizing step can be carried out by, for example,chemical mechanical polishing (CMP). See for example Smekalin et al.,“Tuning the Process Flow to Optimize Copper CMP,” Solid State TechnologyWafer News, Microlithography World. Such planarization steps areconducted for metal interconnects made by the damascene and dualdamascene processes, as will be described in more detail with respect tothe first and second embodiments.

For all of the approaches, the biological peptide may be annealed afterthe seed layer formation step, but before the electroless plating, orafter the electroless plating step, or not at all, depending onapplication and functional need. Annealing can improve conductivity oradhesion. The temperature of annealing can be, for example, about 400°C. or less, or about 300° C. or less, or about 200° C. or less. Theannealing time can be for example at least about 15 minutes, or at leastabout 30 minutes, or at least about 60 minutes. This can, for example,improve resistivity. Furthermore, the anneal can volatilize thebiological agent to remove it from the completed device. It is possiblethat some biological residue remains between the substrate and the seedlayer.

First Embodiment Seeded Barrier Layer Deposition

FIG. 18A shows the completed device of the first embodiment. In thedevice, the planarized copper interconnect 209 is located in electricalcontact with an underlying barrier layer 227 which electrically contactmetallization 109, such as a lower level copper interconnect. Thebarrier layer 227 and the copper interconnect 209 are located in atrench and/or a via in an interlayer insulating layer 211. The barrierlayer 227 is selectively deposited on the nanoparticle based seed layer232, which may comprise a continuous or a discontinuous metal layer.Optionally, peptide residue from the volatilized peptides may be locatedbetween the interlayer insulating layer 211 and the seed layer 232.

A method of forming a seeded barrier layer in a dual damascene processaccording to the first embodiment will be described. While a peptide isused as an example of a biological agent, it should be understood thatthe other biological agents may be used instead.

FIG. 18B shows an interlayer insulating layer 211. The interlayerinsulating layer may comprise one or more inorganic and/or organic(i.e., high-k) insulating sublayers. The interlayer insulating layer 211is provided to separate two interconnect metallization levels or toseparate the lowest interconnect-metallization level and the electrodeswhich contact the semiconductor device. The semiconductor device may beformed on (i.e., over and/or partially in) a silicon wafer or othersupporting substrate (not shown in FIG. 18B). As shown in FIG. 18B,layer 211 is located over an underlying interconnect metallization level109.

The interlayer insulating layer may comprise several organic high-kdielectric sublayers 211A, 211B, such as fluorinated or non-fluorinatedorganic polymer sublayers, separated by inorganic etch stop/hard masksublayers 211C, 211D, 211E, such as silicon nitride sublayers. Sublayer211C is a cap layer for the interconnect 109. Sublayer 211C material mayalso comprise a conductive cap layer, such as a cobalt alloy describedwith respect to the third embodiment if the underlying interconnectmetallization level 109 comprises copper. Sublayer 211D is an etch stopsublayer and sublayer 211E is a hard mask sublayer.

The interlayer insulating layer contains a trench 221. One or more vias223 are located in the trench. As shown in FIG. 18B, the via 223 islocated in the bottom surface of the trench 221 and connects the trench221 to the underlying metallization level 109, which may be anunderlying interconnect metallization level or an electrode contacting asemiconductor device. The trench 221 may be formed first, followed bythe formation of one or more vias 223 in the trench (i.e., atrench-first dual damascene process). Alternatively, one or more vias223 may be formed first, followed by formation of a trench 221 which isconnected to the via(s) (i.e., a via-first dual damascene process). Thetrench and via(s) may be formed by photolithography or other patterningmethods known in the art.

As shown in FIG. 18C, an optional metal plug 225, such as a tungstenplug, is then formed in the via 223 to fill the via. The plug contactsthe underlying metallization 109 that was previously exposed in the via.The plug may be formed using any suitable metal deposition methods, suchas PVD or CVD.

The seed sensitizer 229 is then formed in the trench 221. If the plug225 has been formed in the via 223, then the seed sensitizer 229 islocated in the trench over the plug 225, as shown in FIG. 18D. If theplug 225 has not been formed in the via 223, then the seed sensitizer229 is also formed in the via, as shown in FIG. 18E.

The seed sensitizer 229 comprises a first biological agent 231, such as,for example, a peptide and a material which will subsequently form aseed layer, such as a nanoparticle 232 seed layer. In general, a seedsensitizer is a layer comprising a biological agent bound to a seedlayer material. As described above, the first biological agent 231 maycomprise a peptide which contains a first part 233 which is adapted toselectively bind to the substrate and a second part 235 which is adaptedto bind to the nanoparticles 232. As described above, the biologicalagent 231 may be formed first followed by selectively attaching pre-madenanoparticles 232 to the biological agent or selectively nucleating newnanoparticles 232 on the biological agent. Alternatively, thenanoparticles 232 may already be attached to the biological agent 231when the seed sensitizer 229 is formed.

For example, when the substrate comprises the interlayer insulatinglayer 211, then the first part 233 of the peptide 231 is adapted toselectively bind to the interlayer insulating layer material. In case ofa low-k dual damascene process, if the interlayer insulating layercomprises a low-k organic dielectric covered with an inorganicdielectric hard mask, such as a low-k polymer dielectric covered with asilicon nitride hard mask, then the first part 233 of the peptide 231may be adapted to selectively bind to the low-k polymer dielectric 211Bwhich is exposed in the trench but not to the inorganic hard mask 211Ewhich covers the remaining top surface of the interlayer insulatinglayer. This selectivity would allow selective formation of the seedsensitizer 229 in the trench 221 but not on the top surface of theinterlayer insulating layer 211. If the via 223 is not filled with theplug 225, then it also allows the selective formation of the seedsensitizer 229 on the sidewalls of the via 223.

If desired, a contrast agent layer (also referred to as a non-stick,mask or inhibitor layer) may be formed on the top surface of theinterlayer insulating layer 211. A contrast agent layer may be anybiological, organic or inorganic material which prevents or reduces thebinding of the seed sensitizer 229 and/or of the subsequent metal layersto the insulating layer 211. The contrast agent layer material may havea selective affinity for the interlayer insulating material over themetal layers. For example, the contrast agent layer may comprise apeptide, protein or amino acid layer.

Alternatively, the first part 233 of the peptide 231 is adapted toselectively bind to the entire interlayer insulating layer 211 and theseed sensitizer 229 may be patterned after formation, as describedabove.

Furthermore, an additional biological agent which can selectively bindto the underlying metallization level 109 (if the plug is not present)or to the plug 225 (if the plug is present) may also be added to providea seed sensitizer on the bottom surface of the via 223 or on the plug225, respectively.

The second part 235 of the peptide 231 may be adapted to selectivelybind to nanoparticles 232 and to prevent nanoparticle aggregation. Thenanoparticles 232 may be any nanoparticles which upon annealing form aseed layer for selective deposition of the metal layer, such as thebarrier layer. For example, the nanoparticles may comprise Au, Pd, Ru orNi nanoparticles. The first 233 and the second 235 parts of the peptide231 may be joined to each other by a linker or the first and the secondparts may be joined to each other directly. After the seed sensitizercomprising a plurality of peptides 231 and nanoparticles 232 isdeposited on the substrate, the first parts of the peptides bind atleast to the trench and/or via in the substrate (i.e., directly to theinsulating trench wall material and/or to the exposed portion of theplug or underlying metallization), while the second parts 235 of thepeptides 231 are bound to the nanoparticles 232. The structure is thenannealed to increase the nanoparticle density to complete the seedsensitizer 229 bound to the substrate. Some or all of the peptides maybe volatized during this annealing.

A metal barrier/liner layer 227 is then formed on the seed sensitizer inthe trench 221 such that it covers the bottom surface and the sidewallsof the trench, as shown in FIG. 18F. The barrier layer 227 may bedeposited from a solution using electroless plating techniques, asdescribed above. If the plug 225 has not been formed in the via 223,then the barrier/liner layer 227 may also cover the bottom and sidesurfaces of the via, as shown in FIG. 18F. If the plug 225 has beenformed in the via 223, then the barrier/liner layer 227 is formed overof the plug in the via, as shown in FIG. 18G. The barrier/liner layer227 may comprise Ta, TiN, TiSiN, Ti/TiN, Ta/TaN, W/WN, Ta/TiN, Ti/Wand/or Al. The peptides 231 may be volatilized by annealing beforeand/or after the formation of the barrier layer 227.

The interconnect layer 209, such as a copper interconnect layer, is thendeposited on the substrate. The copper may be deposited from a solutionusing electroless plating techniques, as described above. The copperselectively binds to the barrier layer 227. If desired, a second seedsensitizer may be used to bind the interconnect layer 209 to the barrierlayer 227, as will be described in more detail below. The copper layer209 fills at least the trench. If the tungsten plug 225 is not formed inthe via, then the copper layer 209 also fills the portions of the via223 that are not filled by the barrier layer 227, as shown in FIG. 18H.If the tungsten plug 225 is formed in the via 223, then the copper layer209 in the trench 223 is formed over the plug 225, as shown in FIG. 18I.

If the seed sensitizer 229 is formed non-selectively over the entiresubstrate (i.e., in the trench and over the top surface of theinterlayer insulating layer), then the barrier layer 227 and the copperlayer 209 cover the entire substrate. The barrier layer 227 and thecopper layer 239 are then removed from the upper surface of theinterlayer insulating layer 211 by polishing, such as bychemical-mechanical polishing. If the inorganic dielectric hard mask211E, such as a silicon nitride mask, is present between the uppersurface of the interlayer insulating layer 211 and the copper layer 209and the barrier layer 227, then this hard mask acts as a polish stop.After the polishing step, the copper remains in the trench as theinterconnect metallization, as shown in FIG. 18A. As noted above, thecopper interconnect 209 either extends into the via 223 to electricallycontact an underlying metallization level 109 or electrically contacts aplug 225 located in the via. This completes the dual damascene process.

Alternatively, if the seed sensitizer 229 is formed selectively in thetrench but not on the upper surface of the interlayer insulating layer211, then the barrier layer 227 is selectively formed on the seedsensitizer in the trench and/or in the via. In this case, the polishingstep may be optionally conducted to planarize the resulting copperinterconnect metallization such that the upper surface of the copperinterconnect 209 is planar with the upper surface of the interlayerinsulating layer. This completes the dual damascene process. Asdescribed above, the peptide portion 231 of the seed sensitizer 229 isvolatilized during the process to leave the nanoparticle portion 232 asthe seed layer in the final device. A residue of the peptide portion 231may also remain in the final device. If desired, a seed layer may alsobe used to selectively deposit the plug 225 into the via 223.

Second Embodiment Interconnect Deposition

FIG. 19A shows the completed device of the second embodiment. In thedevice, the planarized copper interconnect 209 is located in electricalcontact with an underlying metallization 109, such as a lower levelcopper interconnect. The copper interconnect 209 is located in a trenchand/or a via in an interlayer insulating layer 211. The interconnect 209is selectively deposited on the nanoparticle based seed layer 232, whichmay comprise a continuous or a discontinuous metal layer. Optionally,peptide residue from the volatilized peptides may be located between theinterlayer insulating layer 211 and the seed layer 232. While a copperinterconnect is illustrated, it should be understood that other metallayers, such as nickel or gold may be used instead.

A method of forming a seeded interconnect layer in a dual damasceneprocess according to the second embodiment will be described. While apeptide is used as an example of a biological agent, it should beunderstood that the other biological agents may be used instead.

FIG. 19B shows an interlayer insulating layer 211, which is the same aslayer 211 shown in FIG. 18B and described above with respect to thefirst embodiment. The interlayer insulating layer contains a trench 221.One or more vias 223 are located in the trench. As shown in FIG. 19C, anoptional metal plug 225, such as a tungsten plug, is then formed in thevia 223 to fill the via.

A metal barrier/liner layer 227 is then optionally formed in the trench221 such that it covers the bottom surface and the sidewalls of thetrench. If the plug has not been formed in the via 223, then thebarrier/liner layer 227 may also cover the bottom and side surfaces ofthe via, as shown in FIG. 19D. If the plug 225 has been formed in thevia 223, then the barrier/liner layer 227 covers the exposed upperportion of the plug in the via, as shown in FIG. 19E. The barrier/linerlayer may comprise Ta, TiN, TiSiN, Ti/TiN, Ta/TaN, W/WN, Ta/TiN, Ti/Wand/or Al. As discussed with respect to the first embodiment, thebarrier layer 227 may be formed using a seed sensitizer which includes apeptide and nanoparticles. Alternatively, the barrier layer 227 may beformed using conventional semiconductor deposition methods, such as CVD,sputtering, plating, etc. If desired, the barrier layer 227 may beomitted.

The seed sensitizer 229 is then formed in the trench 221. If the plug225 has not been formed in the via 223, then the seed sensitizer 229 isalso formed in the via, as shown in FIG. 19F (optional layer 227 isomitted for clarity from this figure). If the plug 225 has been formedin the via 223, then the seed sensitizer 229 is located in the trenchover the plug 225, as shown in FIG. 19G. If the barrier/liner layer 227is present, then the seed sensitizer 229 is formed over thebarrier/liner layer 227.

The seed sensitizer 229 comprises a first biological agent 231, such as,for example, a peptide, and nanoparticles 232. As described above, thefirst biological agent 231 may comprise a peptide which contains a firstpart 233 which is adapted to selectively bind to the substrate and asecond part 235 which is adapted to bind to the nanoparticles 232.

For example, when the substrate comprises the interlayer insulatinglayer 211 which does not contain the barrier/liner layer 227, as shownin FIG. 19F, then the first part 233 of the peptide 231 is adapted toselectively bind to the interlayer insulating layer material. In case ofa low-k dual damascene process, if the interlayer insulating layercomprises a low-k organic dielectric covered with an inorganicdielectric hard mask, such as a low-k polymer dielectric covered with asilicon nitride hard mask, then the first part 233 of the peptide 231may be adapted to selectively bind to the low-k polymer dielectric 211Bwhich is exposed in the trench but not to the inorganic hard mask 211Ewhich covers the remaining top surface of the interlayer insulatinglayer. This selectivity would allow selective formation of the seedsensitizer 229 in the trench 221 but not on the top surface of theinterlayer insulating layer 211. If the via 223 is not filled with theplug 225, then it also allows the selective formation of the seedsensitizer 229 on the sidewalls of the via 223. Alternatively, the firstpart 233 of the peptide 231 is adapted to selectively bind to the entireinterlayer insulating layer 211 and the seed sensitizer 229 may bepatterned after formation, as described above. In the case where thebarrier layer 227 is not included, an additional peptide which canselectively bind to the underlying metallization level 109 (if the plugis not present) or to the plug 225 (if the plug is present) may also beadded to provide a seed sensitizer on the bottom surface of the via 223or the plug 225, respectively.

If desired, a contrast agent layer described above may be formed on thetop surface of the interlayer insulating layer 211. A contrast agentlayer may be any biological, organic or inorganic material whichprevents or reduces the binding of the seed sensitizer 229 and/or of thesubsequent metal layers to the insulating layer 211.

In another example, if the substrate comprises the metal barrier/linerlayer 227 located in the trench 221 and/or the via 223 in the interlayerinsulating layer 211, as shown in FIG. 19G, then the first part 233 ofthe peptide 231 is adapted to selectively bind to the metalbarrier/liner layer 227, but not to the interlayer insulating layer 211.This selectivity would allow selective formation of the seed sensitizer229 on the metal barrier/liner layer 227 in the trench and/or via butnot on the top surface of the interlayer insulating layer 211.

The second part 235 of the peptide 231 may be adapted to selectivelybind to nanoparticles 232 and to prevent nanoparticle aggregation. Thenanoparticles 232 may be any nanoparticles which upon annealing form aseed layer for selective deposition of the metal layer. For example, forCu layer formation, the nanoparticles may comprise Cu, Au, Pd, Ru or Ninanoparticles. The first 233 and the second 235 parts of the peptide 231may be joined to each other by a linker or the first and the secondparts may be joined to each other directly. After the seed sensitizercomprising a plurality of peptides 231 and nanoparticles 232 isdeposited on the substrate, the first parts of the peptides bind atleast to the trench and/or via in the substrate (i.e., directly to theinsulating trench wall material and/or to the conductive barrier/linermaterial in the trench), while the second parts 235 of the peptides 231are bound to the nanoparticles 232. The structure is then annealed toincrease the nanoparticle density to complete the seed sensitizer 229bound to the substrate. Some or all of the peptides may be volatizedduring this annealing.

The copper interconnect layer 209 is then deposited on the substrate.The copper may be deposited from a solution using electroless platingtechniques, as described above. The copper selectively binds to the seedsensitizer 229. In other words, the copper selectively binds to themetal nanoparticle 232 containing seed sensitizer 229. The peptides 231may be volatilized by annealing before and/or after the formation of thecopper layer 209. The copper layer fills at least the trench. If thetungsten plug 225 is not formed in the via, then the copper layer 209also fills the via 223 in addition to the trench 221, as shown in FIG.19H. If the tungsten plug 225 is formed in the via 223, then the copperlayer 209 in the trench 223 electrically contacts the plug, as shown inFIG. 19I.

If the seed sensitizer 229 is formed non-selectively over the entiresubstrate (i.e., in the trench and over the top surface of theinterlayer insulating layer), then the copper layer 209 covers theentire substrate. The copper layer 209 is then removed from the uppersurface of the interlayer insulating layer by polishing, such as bychemical-mechanical polishing. If the inorganic dielectric hard mask211E, such as a silicon nitride mask, is present between the uppersurface of the interlayer insulating layer 211 and the copper layer 209,then this hard mask acts as a polish stop. After the polishing step, thecopper remains in the trench as the interconnect metallization, as shownin FIG. 19A. As noted above, the copper interconnect 209 either extendsinto the via 223 to electrically contact an underlying metallizationlevel 209 or electrically contacts a plug 225 located in the via. Thiscompletes the dual damascene process.

Alternatively, if the seed sensitizer 229 is formed selectively in thetrench but not on the upper surface of the interlayer insulating layer211, then the copper layer 209 is selectively formed on the seedsensitizer in the trench and/or in the via. In this case, the polishingstep may be optionally conducted to planarize the resulting copperinterconnect metallization such that the upper surface of the copperinterconnect 209 is planar with the upper surface of the interlayerinsulating layer. This completes the dual damascene process.

Third Embodiment Cap Layer

In a third embodiment of the invention, a cap layer and a method offorming a cap layer are provided. The formation of the cap layer can beadapted depending on the particular application and applicationrequirements. For example, the cap layer thickness and composition maybe selected to reduce electromigration damage and to extend theelectromigration lifetime of a conductive layer, such as a copperinterconnect formed over a solid state device, such as a semiconductordevice. Thus, the material, thickness and characteristics of the caplayer may be selected to provide optimal enhancement of electromigrationlifetime of the underlying metal layer.

The cap layer can be made of any material effective in reducingelectromigration damage in a metal layer, such as in a copperinterconnect. The use of cap layers and effective cap layer materialsare known in the art as evidenced by the following references, which areeach incorporated by reference in their entirety: Hu et al., RELIABILITYPHYSICS SYMPOSIUM PROCEEDINGS, 42^(nd) Annual (2004 IEEE International);Kohn et al., JOURNAL OF APPLIED PHYSICS 92(9):5508-5511 (2002); and U.S.Pat. No. 6,605,424. Examples of materials known to be effective cappingmaterials include silicon nitride (SiN_(x)), Ta/TaN, silicon carbides(including SiC and SiC_(x)N_(y)H_(z)), cobalt alloys and nickel alloys.Cobalt alloys include Co—P or Co—B alloys which may further contain oneor more of W, Mo and/or Re (i.e., rare earth alloying element(s)). Forexample, the cobalt alloys include CoMoP, CoReP, CoP, CoWB and CoWPalloys, such as Co_(0.9)W_(0.02)P_(0.08) and Co_(0.9)P_(0.1). Nickelalloys include NiP or NiB alloys which may also contain one or more ofCu, Pd, Co, W, Mo and/or Re, such as NiCuP, NiPdP, NiCoP, NiWP, NiMoP orNiReP. More than one type of material can be used to form the cap layer.For example, one or more of Ta, Ru, Ti, W, titanium nitride and/ortantalum nitride can be used together with a cap layer material which isdeposited by plating.

The cap layer is formed using a seed sensitizer comprising at least onebiological agent, such as those described herein. For example, thebiological agent can be a peptide or a bifunctional amino acid. Othertypes of biological agents described above may also be used. Thebiological agent has at least one binding site moiety or domain (i.e., afirst part), which selectively binds to a conductive material, such asCu. The biological agent may be selected so that it doesn'tsubstantially bind to background material, such as the dielectricmaterial of the interlayer insulating layer. For example, in someembodiments less than 5% of biological agent binds to backgroundmaterial, in some embodiments less than 2% of biological agent binds tobackground material, and in some embodiments less than 1% of biologicalagent binds to background material. Alternatively, the biological agentmay be selectively deposited by stamping or it may be deposited on theentire substrate followed by pattering. In this case, the biologicalagent does not necessarily have to have a binding site moiety or domainwhich selectively binds to the underlying metal layer.

The biological agents can be produced by any method. Such methods offorming biological agents with material binding specificity and examplesof specific biological agents are known in the art, as evinced by thereferences cited herein. For example, peptide libraries and biopanningcan be used to select biological agents for use in forming the caplayer.

In addition to binding to the conductive material, the biological agentis also selected to direct the formation of the cap layer by directingthe formation of a cap seed layer. Such a bifunctional biological agentcan be referred to as a sensitizer. The cap material can then beselectively deposited on the cap seed layer. Accordingly, thenanoparticle seed layer material is selected to allow the selectiveformation of the cap layer on the cap seed layer. Examples ofnanoparticles that can be used for the cap seed layer include Au, Pd,Ru, Ni, Fe, Rh, Co and their alloys, such as Co, CoP, CoWP, CoB, CoWB,CoPd, CoPt, etc. The nanoparticles can bind to the biological agenteither before or after the biological agent is applied to the conductivematerial, such as the copper interconnect. For example, preformednanoparticles may be placed in contact with the biological agent.Alternatively, the biological agent can also be selected to nucleate thenanoparticles from one or more precursor materials, as described above.The use of biological agents to form nanoparticles is known in the art,such as the references cited herein. The nanoparticle cap seed layer canbe fused, such as by a thermal process, either before or after thedeposition of the cap material.

FIGS. 20A-20D illustrate a method of forming the cap layer on a metallayer according to the second aspect of the second embodiment. As shownin FIG. 20A, the biological agent 231, such as a peptide is formed froma first part or construct 233 having a binding affinity for copper orother interconnect metal and a second part or construct 235 having abinding affinity for nanoparticles 232 which can act as a nucleationseed for a cap layer. The parts 233 and 235 may be coupled directly toeach other or by using a linker. The nanoparticles 232 may be coupled topart 235 (i.e., binding site 235) of agent 231 by combining thebiological agent 231 with a nanoparticle precursor solution 201. Thus, aseed sensitizer comprising biological agent capped nanoparticles isformed in the solution. Alternatively, the biological agent can bepre-adsorbed and then used to “capture” ions or pre-formed nanoparticles(such as metal ions or nanoparticles) from solution.

As shown in FIG. 20B, the seed sensitizer 229 is deposited on asubstrate. The substrate contains the copper interconnect 209 or anotherconductive layer at least in a trench in the interlayer insulating layer211. For example, the seed sensitizer 229 can be provided from asolution and/or formed into a dispersion. The solution or dispersion canthen be applied to the substrate, such as by spraying the dispersiononto the substrate.

As shown in FIG. 20C, the deposition of the seed sensitizer 229 isfollowed by a washing step to remove the seed sensitizer from theinterlayer insulating layer 211 while leaving the seed sensitizer 229mostly bound to the copper interconnect 209 due to the binding affinityof the part 233 of the seed sensitizer to copper. The washing can beperformed using any solvent that is compatible with the substrate, thatwill not substantially disrupt the binding of the seed sensitizer 229 tothe interconnect 209.

Alternatively, the seed sensitizer 229 may be formed by selectivestamping and/or by coating following by patterning. If desired, acontrast agent layer described above may be formed on the top surface ofthe interlayer insulating layer 211. A contrast agent layer may be anybiological, organic or inorganic material which prevents or reduces thebinding of the seed sensitizer 229 and/or of the subsequent metal layersto the insulating layer 211.

As shown in FIG. 20D, the prepared surface of the substrate is exposedto a cap layer precursor solution, such as a cobalt alloy electrolessplating solution. The cap layer precursor material may comprise anelectroless plating solution, such as a Co—W—P or Co—P aqueous solutioncomprised of metallic ion complexes and a reducing agent, such as sodiumhypophosphite, as described for example in Kohn et al., Microelectron.Eng. 55, (2001) 297 and Kohn et al., Mater. Sci. Eng. A302 (2001) 18,incorporated herein by reference.

The cap layer 213 is selectively formed on the copper interconnect 209due to the binding affinity of the nanoparticles 232 of the seedsensitizer 229 to the cap layer material. The cap layer 213 formationmay be followed by an annealing step to remove the biological agent 231and to enhance the adhesion of the cap layer 213 to the interconnect209. As described above with respect to the first and secondembodiments, a residue of the biological agent, such as a peptideresidue may remain in the device.

In another aspect of the third embodiment, the nanoparticles 232 of theseed sensitizer 229 comprise the whole cap layer 213 or a bottom portionof the cap layer. Thus, the nanoparticles are made of a material thatcan act as an effective cap layer. The nanoparticle cap layer can befurther enhanced with an additional cap layer. The additional cap layercan be the same or different than the nanoparticle material. Forexample, the nanoparticles can be cobalt or cobalt alloy nanoparticlesand the enhancement layer can be a cobalt alloy layer, such as CoWP.Together, the nanoparticles and the overlying enhancement layer form thecap layer. The cap layer can be placed on an upper surface of the copperinterconnect and/or on any exposed side surface of the interconnect.

Seeded and Capped Dual Damascene Copper Interconnect

FIG. 21 shows a completed seeded and capped dual damascene copperinterconnect structure. Reference numbers 232A, 232B and 232C show thepossible location of the fused nanoparticles of the seed layers and thebiological agent residue, such as a peptide residue, which are used toselectively deposit the metal layers. Thus, the fused nanoparticlesand/or the peptide residue may be located in any one, two or all threelocations. Furthermore, if a biological contrast agent is used, thencontrast agent residue 241 may be located on top of the interlayerinsulating layer.

Seeded Display Device Bus Line

While a dual damascene interconnect was used as an example ofbiologically seeded deposition, metal layers in other electronic devicesmay also be formed using the biologically seeded method. For example,FIG. 22 shows an example of a display device bus or conductor line whichis formed using a biological seed layer. The bus line may be formed inany suitable display device, such as a liquid crystal display (LCD),plasma display, LED display or organic light emitting diode (OLED)display.

As shown in FIG. 22, the bus line 309 is formed over a substrate 301,such as a glass, plastic, quartz or other transparent or non-transparentsubstrate. The bus line 309 may connect devices, such as transistors inan active matrix configuration to driver circuits. In this case, theseed sensitizer 229 may be formed on the substrate 301 in a bus linepattern using stamping or patterning. The bus line 309 is thenselectively formed on the seed sensitizer 229. For example, the bus linemay comprise an electrolessly plated copper layer 310 selectively formedon the seed sensitizer and a nickel layer 312 selectively formed on thecopper layer by electroless plating or other methods. Thus,photolithographic patterning of the metal layers of the bus line 309 isnot required.

After annealing, the peptide portion of the seed sensitizer isvolatilized. The completed display device includes the bus line 309formed on a fused nanoparticle seed layer 232 portion of the seedsensitizer 229, as shown in FIG. 22. A peptide residue may be locatedbetween the substrate 301 and the fused nanoparticle layer 232.

The compositions and methods described herein can be used in dualdamascene and other metal deposition processes. The metal layersdescribed above may be used in various solid state devices, such asoptically active films, OLEDs, active matrix liquid crystal displays(AMLCD) (as described in, for example, U.S. Pat. No. 6,887,776) andother displays, and semiconductor devices including memory devices, suchas DRAM, PROM, EPROM and EEPROM, logic devices, such as ASICs andmicroprocessors, light emitting devices, such as LEDs and lasers andlight receiving devices, such as photodetectors and solar cells.Furthermore, while formation of copper layers were specificallydescribed, copper, nickel, gold, platinum, cobalt, silver, palladium,ruthenium, rhodium or alloys thereof can also be made.

Plating Bath Composition

Any suitable plating baths may be used. For example, a CoWP plating bathto plate a CoWP cap layer may have the following recipe:

0.03˜0.15 M Co(OH)₂,

0.05˜0.3 M H₃PO₂,

0.1˜0.5 M Na₃C₆H₅O₇,

0.3˜0.6 M H₃BO₃,

0.01˜0.08 M Na₂WO₄,

NH₄OH adjusting pH to 8.0˜10.0, 65˜85° C.

More generally, a plating bath having the following recipe can be used:

a cobalt salt (Co²⁺) such as, without limitation, CoSO₄, CoCl₂ orCo(OH)₂,

a reducing agent, such as a hypophosphite salt (H₂PO₂ ⁻) such as,without limitation, H₃PO₂, NaH₂PO₂, KH₂PO₂ or NH₄H₂PO₂,

a metal chelator, such as a citrate salt (C₆H₅O₇ ³⁻) such as, withoutlimitation, H₃C₆H₅O₇, Na₃C₆H₅O₇ or K₃C₆H₅O₇,

a buffer, such as, without limitation, H₃BO₃, ethanolamine, TAPS,bicine, or CHES, and

a tungstate salt (WO₄ ²⁻) such as, without limitation, Na₂WO₄, K₂WO₄, or(NH₄)₂WO₄.

Preferably, the ratio of the molar concentrations of the cobalt salt tothe reducing agent (hypophosphite salt) is from 1:3 to 1:5 and the ratioof the molar concentrations of the cobalt salt to the metal chalator(citrate salt) is from 1:2.5 to 1:3.5. If desired, a metal chelatorother than the citrate salt may be used. Examples of other metalchelating agents are:

-   (ethylenedinitrilo)tetraacetic acid (EDTA),-   butylenediaminetetraacetic acid,-   (1,2-cyclohexylenedinitrilo)tetraacetic acid (CyDTA),-   diethylenetriaminepentaacetic acid,-   ethylenediaminetetrapropionic acid,-   (hydroxyethyl)ethylenediaminetriacetic acid (HEDTA),-   N,N,N′,N′ ethylenediaminetetra(methylenephosphonic)acid (EDTMP),-   triethylenetetraminehexaacetic acid (TTHA),-   1,3-diamino-2-hydroxypropane-N,N,N′,N′-tetraacetic acid (DHPTA),-   methyliminodiacetic acid, propylenediaminetetraacetic acid,-   1,5,9-triazacyclododecane-N,N′,N″-tris(methylenephosphonic acid)    (DOTRP),-   1,4,7,10-tetraazacyclododecane-N,N′,N″,N′″-tetrakis(methylenephosphonic    acid)-   (DOTP), nitrilotris(methylene)triphosphonic acid,-   diethylenetriaminepenta(methylenephosphonic acid) (DETAP),-   aminotri(methylenephosphonic acid),-   1-hydroxyethylene-1,1-diphosphonic acid,-   bis(hexamethylene)triamine phosphonic acid,-   1,4,7-triazacyclononane-N,N′,N″-tris(methylenephosphonic acid    (NOTP),-   2-phosphonobutane-1,2,4-tricarboxylic acid,-   nitrolotriacetic acid (NTA),    various salts and free acid of citric acid, tartaric acid, gluconic    acid, saccharic acid, glyceric acid, oxalic acid, phthalic acid,    maleic acid, mandelic acid, malonic acid, lactic acid, salicylic    acid, 5-sulfosalicylic acid, catechol, and gallic acid propyl    gallate, pyrogallol, 8-hydroxyquinoline, and cysteine.

Better selectivity was observed when coupling the cysteine PdCl₂sensitization process with an electroless cobalt solution in which thehypophosphite to cobalt ratio was about 3 or greater. The selectivitywas assessed by examining plated films using a scanning electronmicroscope to locate areas in which plating occurred in the spacesbetween copper lines, i.e. on the low-k dielectric. In addition, thedeposited metal film morphology was smooth, continuous and nodule-freewhen the hypophosphite to cobalt ratio was about 3 or greater, whereas amore granular and discontinuous film with nodules was typical of filmsplated with lower hypophosphite to cobalt ratios.

In certain applications, it is advantageous to use an alkali freeplating solutions since the alkali metal ions (potassium or sodium)present in the solution may act as main mobile ionic contaminants. Inparticular, the metallic ions can move inside the device, causing adevice to fail, as is described in U.S. Pat. No. 6,797,312.Additionally, it is known in the art that halogens can have detrimentaleffects semiconductor fabrication, thus, it can be advantageous to use ahalogen free plating solution.

The following composition ranges of alkali-free bath solution can beused:

0.03˜0.15 M Co(OH)₂,

0.05˜0.3 M H₃PO₂,

0.1˜0.5 M (NH₄)₃C₆H₅O₇,

0.3˜0.6 M H₃BO₃,

0.01˜0.08 M H₂WO₄

NH₄OH adjusting pH to 8.0˜10.0 at 70˜85° C.

One example of the alkali free bath solution is:

0.062 M Co(OH)₂,

0.25 M H₃PO₂,

0.5 M (NH₄)₃C₆H₅O₇,

0.4 M H₃BO₃,

0.03 M H₂WO₄,

NH₄OH adjusting pH to 9.0˜9.5 at 80˜85° C.

Thus, the bath contains NH⁴⁺ instead of Na⁺ ions. One hour plating oncopper surfaces shows a typical composition of Co (91%) W (2%) P (7%)and a good plating selectivity on a 300 nm copper line.

More generally, an alkali-free bath solution having the followingcomposition may be used:

a cobalt salt (Co²⁺) such as, without limitation, CoSO₄ or Co(OH)₂,

reducing agent, such as a hypophosphite salt (H₂PO₂ ⁻) such as, withoutlimitation, H₃PO₂ or NH₄H₂PO₂,

(NH₄)₃C₆H₅O₇,

a buffer, such as, without limitation, H₃BO₃, ethanolamine, TAPS,bicine, or CHES, and

a tungstate salt (WO₄ ²⁻) such as, without limitation, (NH₄)₂WO₄.

Preferably, the ratio of the molar concentrations of the cobalt salt tothe reducing agent (i.e., hypophosphite salt) is from 1:3 to 1:5 and theratio of the molar concentrations of the cobalt salt to the (NH₄)₃C₆H₅O₇is from 1:2.5 to 1:3.5. If desired, an alkali free metal chelator otherthan (NH₄)₃C₆H₅O₇ may be used. Alkaki free baths may also be used toplace CoP, CoWB and other layers.

WORKING EXAMPLES

The invention is further illustrated with use of the followingnon-limiting working examples.

Example 1 Formation of Au Nanoparticles in the Presence of Peptides

A gold precursor salt, HAuCl₄ (2 mM), was interacted with 100 μM ofdesired peptide in 100 mM Tris-acetate buffer at pH 7.5. NaBH₄ aliquotswere added over 30-60 min, and spectral changes were measured todetermine size of Au nanoparticles being formed. Peptides includedpeptides 1, 2, 3, and 3222A/B. FIGS. 1A and 1B provide TEMcharacterization of gold nanoparticles and plot of nanoparticle diameterdistribution.

Example 2 Formation of Pd Nanoparticles in the Presence of Peptides

A palladium precursor salt, K₂PdCl₄ (which produces a Pd complex ion,PdCl₄ ²⁻) was interacted with peptides in buffer solutions. NaBH₄aliquots were added over 30-60 min. Stable colloidal solutions wereobtained and were further processed by gel filtration. Peptides includedpeptides 1, 2, 3, and 3222A/B.

Example 3 Ligand Exchange of Gold Nanoparticles with Peptide

Peptides were diluted 1:50 into Au nanoparticle solution to form a 100μM final concentration of peptide. The mixture was allowed to incubateat room temperature for 30 minutes. The solution was then concentratedby centrifugation at 14,000 r.p.m., and the supernatant was removed. Theexcess free peptide was then removed and buffers (or water) exchangedusing NAP-5 size exclusion purification exchange columns as supplied.

Example 4 Using an Au Seed Layer to Form a Au Film

On a Corning 1737 glass substrate (6×6 mm) was adsorbed 5 μMStreptavidin in 100 mM Hepes (pH 7.5). The streptavidin was soaked withthe glass chips in an Ependorff tube for 1 hour w/gentle rocking. Eachglass substrate was washed 2× with deionized water. A seed layer ofnanoparticles was then added to the substrate through a streptavidin(surface)-biotin (peptide) interaction. A 1:5 dilution of size exclusiongel filtered nanoparticles in H₂O (originally formed from 2 mM HAuCl₄,gold nanoparticles formed using biotinylated peptide 2 & peptide 3) wasincubated for 30 minutes on the glass substrate to bind the Aunanoparticles forming the seed layer. The layer was rinsed with DIwater. The seed layer on glass was then incubated for 5 minutes with anElectroless Plating (EP) solution (GoldEnhance), forming a metal film.The film was washed with DI water, then an optional second EP step wasperformed by pipetting 50 μl of solution onto the 1737 glass chips. Thefilm was again rinsed with DI water, then imaged by AFM and opticalmicroscopy.

FIG. 3 shows images of the Au seed layer for the first EP step followedby a second. Grain size analysis of these images (shown in FIG. 4),reveal an increase in grain size after the second EP step. These imagescombined show a biologically directed Au thin film.

The film did not grow without the seed layer or the peptide.

Example 5 Patterning

Additionally, placement of the peptide coated nanoparticles directly(without using streptavidin-biotin) on the glass substrate was performedusing a microcontact printing approach. A polydimethylsiloxane (PDMS)stamp was purchased (Platypus Technologies) and prepared by incubationwith gold nanoparticles synthesized with biotinylated Peptide 2 (1:5dilution) for 1 hour (peptide 2 exhibits a high affinity toward glass).The stamp was then rinsed with water and dried with nitrogen. The Aunanoparticle laden stamp was then printed onto a glass microscope slideand imaged via optical microscopy. When the glass substrate was imagedwith the printed seed layer, the pattern conveyed by the stamp wasimmediately apparent (FIG. 5).

The glass substrate with the printed substrate was further processed byone application (15 minutes) of the electroless plating solution(GoldEnhance). The gold film was immediately visible, as shown on thefar right image in FIG. 6. Optical microscopy images of the electrolessplated pattern (images left, FIG. 6) show clear resolution of theprinted pattern. One interesting point is that the resolution of theseed was preserved in the subsequent plating experiments, at least tothe degree to which the line widths could be measured. Further analysisof the patterned film by AFM revealed a gold film thickness of 130.5 nm(FIG. 7).

The same printed Au-peptide 2 seed was also used to form a copper filmby electroless plating (FIG. 8) using the Transene pH 13 solution.

Example 6 Using a Pd Seed Layer to Form a Cu Film

Palladium nanoparticles were synthesized in the presence of biotinylatedCALNN peptide (SEQ ID NO: 1). The peptide coated nanoparticles were theninteracted with glass substrates coated with Poly-lysine or withStreptavidin. After interaction with the glass, which deposited the Pdseed layer, two different Cu plating solutions were used to evaluateeffectiveness of Cu film formation (Transene pH 13 solution and an IBMpH 9 solution). Other parameters were also varied during the electrolessplating step, including time, temperature, agitation, glass substratecleaning, and peptide used to mediate nanoparticle formation.

FIG. 9 shows images of Cu films grown on Pd seed layers on streptavidincoated glass substrate using a pH13 EP solution. Time and temperaturedid play a role in the thickness and adhesive properties of the filmgrown. When no Pd seed layer was present, no Cu film was formed. FIGS.10 and 11 show resultant Cu films grown from pH9 EP solutions on Pdseeds on streptavidin or poly-lysine coated glass substrates.

Example 7 Using an Au Seed Layer and Enhancing with Electroless Platingto Form a Cu Film

Cu films were fabricated by incubating a Corning 1737 glass substratewith Au nanoparticle (Peptide 2 stabilized) solution for ten minutesforming a seed layer on the glass. The seed layer was then annealed for20 minutes at 200 C. This process gives a very dense seed. This seedlayer, both pre- and post-annealing step was studied by Atomic ForceMicroscopy. Analysis of surface area roughness (as shown in FIG. 12)shows that annealing does not change the structure of the seed layer,although the resultant Cu film grows better on an annealed seed layer,it is believed that annealing strengthens seed layer adherence to thesubstrate in preparation for the high pH electroless plating step.

A Cu film was then grown on the annealed seed layer using a copperelectroless plating solution (Transene) for 2.5-4 minutes. Cu filmsgrown in this manner are shown in FIG. 13.

Film thickness and resistivity measurements were then measured by atomicforce microscopy and a four point probe station. This AFM analysis isshown in FIG. 13. Thicknesses measured were 70 nm and 100 nm.Resistivity measurements taken were 14 μΩ-cm and 10 μΩ-cm. Note thatsince a four point probe station was used, the resultant measurementsare overestimates of the resistivity of sample due to edge effects.

During these experiments, differing purification processes of the Aunanoparticles used were performed to see if the seed layer influencedthe resultant Cu film that was ultimately grown. FIG. 14 shows thatcopper films were still formed when using Au nanoparticles that had beenpurified by ultra-filtration prior to introduction to the glasssubstrate.

Additionally, this Cu film growth on a Au seed layer was tried on atantalum nitride substrate. The TaN substrate was 100 nm thick and wasdeposited as a film on SiO₂ by sputtering at −50° C. Sputtering of TaNwas done by reactive sputtering of Ta in nitrogen gas. It is believedthat the substrate had an atomic ratio of Ta to N of about 1.5-2 to 1.The TaN was used as supplied and was incubated for 20 minutes with Au(Peptide 2) nanoparticle solution in 0.1×PBS. The resultant seed layerwas then annealed at 200 degrees C. for 20 minutes. A Cu film (FIG. 16)was then grown on the seed layer using an electroless plating solution(Transene) for 3.5 minutes.

AFM analysis of the Cu film grown on TaN was performed. Section analysis(FIG. 17 left) of the film showed a thickness of 85 nm. Surfaceroughness analysis (FIG. 17 right) showed a roughness of 4 nm, similarto films grown on glass.

Example 8 Using a Small Bifunctional Molecule to Form a Cap Layer

While peptides were described above as one example of a biologicalagent, other materials may be used instead. For example, smallbifunctional organic molecules may be used in the selective formation ofthe metal layer. The bifunctional organic molecules may comprisebifunctional amino acid molecules where one functionality interactsspecifically with part of the patterned substrate while the secondfunctionality interacts with a sensitizer agent (i.e., the material ofthe seed layer) for the plating chemistry. The term “bifunctionalmolecule” means a single molecule with two or more functional regions.

In the present example, the bifunctional amino acid molecule is acysteine which is used to nucleate the cap layer for a copperinterconnect, bus line or another electrode. As shown in FIG. 23,cysteine has a first functionality which selectively binds to thepatterned copper layer but which does not selectively bind to theorganic, low-k dielectric layer in which the copper layer is embedded.Cysteine also has a second functionality which binds to a platingsensitizer agent, such as metal ions from a solution (for example Pd⁺⁺ions which form a Pd sensitizer) or metal nanoparticles from a solutionor suspension (for example Pd or Co nanoparticles), as shown in FIG. 23.

It is believed that the use of small bifunctional molecules allows asignificantly lower concentration of Pd sensitizer agent than a priorart plating method to selectively plate a cobalt alloy cap layer, suchas a CoP, CoWP or CoWB (from a stored CoWB bath) cap layer over a copperpattern. Since the Pd sensitizer agent is expensive, this decreases thecost of the process. Also, selectivity is improved since lowerconcentrations of the Pd sensitizer lead to less non-specific adsorptionof the Pd sensitizer agent and subsequently more selective plating ofthe Co alloy onto both the copper and the dielectric regions on thewafer. With the use of the small bifunctional molecules, the sensitizeragent concentration is reduced to levels that are believed to begenerally insufficient to catalyze the plating reaction with the priorart methods. For example, cysteine allows the use of 10 ppm or less ofPdCl₂ in 0.5 M H₂SO₄, such as 5 ppm or less, for selective CoP and CoWB(from a stored CoWB bath) plating over a copper pattern. In contrast, inthe prior art methods, it is believed that a greater concentration ofPdCl₂ in 0.5 M H₂SO₄ is required for selective CoP and CoWB (from astored bath) deposition over a copper pattern. It should be noted thatwhile the present example illustrates plating of CoWB and CoP on Pdsensitizer agent, other metals, such as cobalt alloys which can beselectively plated on a Pd sensitizer agent may also be used. Suchcobalt alloys include CoWP. It should also be noted that theconcentration of PdCl₂ described herein refers to a concentration ofPdCl₂ in 0.5 M H₂SO₄. This PdCl₂ can be converted to concentration of Pdusing the following formula: ppm Pd=0.6×ppm PdCl₂.

Furthermore, high sensitizer agent concentration in the prior artmethods may lead to non-selective deposition of the sensitizer agent(i.e., the sensitizer agent is deposited on the entire substrate ratherthan just on an underlying metal pattern). This means that a subsequentmetal plating step, such as a CoP cap layer plating step, is also notselective. Thus, the bifunctional molecules improve the selectivity ofthe deposition of the cap layer. Without wishing to be bound to aparticular theory, it is believed that the enhanced selectivity may bedue to the concentration dependence of standard adsorption isotherms.Lower Pd concentration may provide a more favorable placement of thePd⁺⁺/low-k dielectric adsorption isotherm. Furthermore, if the cap layeris used as a seed for the selective deposition of overlyingmetallization, such as upper level barrier and/or copper interconnectmetallization, then the selectivity of the deposition of the upper levelmetallization is also improved.

In the general method of the present example, the deposited copper layeris exposed to the sensitizer agent and localizes the deposition of thesensitizer agent. The cap layer is then selectively plated in the areascontaining the sensitizer, as shown in FIG. 23.

Specifically, an exemplary process for CoWB plating includes thefollowing steps:

-   -   1. Clean the Cu surface (1 min. in pH 10 NaOH, DI rinse, 1 min.        in 2% H₂SO₄, DI rinse);    -   2. Cysteine adsorption (30 sec.-60 sec.): 10 mM cysteine in 0.5        M H₂SO₄;    -   3. DI rinse;    -   4. Pd activation (30 sec.-45 sec.): 25 ppm or 10 ppm PdCl₂ in        0.5 M H₂SO₄;    -   5. DI rinse;    -   6. Plate CoWB (1 min.): 0.1 M CoSO₄, 0.3 M (NH₄)₃C₆H₅O₇, 0.03 M        H₂WO₄, 0.06 M DMAB, (bath stored for more than 12 hours);    -   7. DI rinse, N₂ drying;    -   8. Optional annealing (2 min.): 250° C. in N₂.

In the method described above, the cysteine is first provided onto theCu surface followed by contacting the cysteine which is bound to the Cusurface with the Pd containing solution.

It should be noted that the solvents, concentrations and process stepduration times are merely illustrative and are not considered limitingon the scope of the invention. It is believed that a fresh CoWB platingbath can plate directly on copper surfaces. However, if the bath isstored for more than 12 hours, it becomes less active and does not plateon copper surfaces without adding a Pd sensitizer agent (i.e., Pdplating catalyst) on the copper surface. Thus, if the CoWB plating bathand the semiconductor device are made by different companies, then thetransport time of the CoWB bath between the bath manufacturer and theend user reduces the activity of the bath and requires the use of asensitized copper surface for plating.

FIG. 24 shows an exemplary micrographs in which the use of a sensitizeragent comprising 10 ppm PdCl₂ in 0.5 M H₂SO₄ (which corresponds to 6 ppmPd) together with cysteine resulted in the selective plating of a CoWBcap over a copper pattern using the above method. It can be seen fromFIG. 24 that less than 10 ppm of PdCl₂ sensitizer agent is sufficient toselectively plate a CoWB cap layer over a copper pattern.

FIGS. 25A-25C further illustrate the effect of cysteine on CoWB caplayer formation. FIG. 25A shows Cu and Co maps and a correspondingintegrated EDX results for a control wafer containing Cu patterns. No Copeak is observed in the EDX spectra. FIG. 25B shows the results of 10ppm PdCl₂ sensitizer agent activation followed by CoWB plating withoutthe use of cysteine according to a prior art method. No Co peak isobserved in the EDX spectra indicating that CoWB did not plate. Thus,the prior art method which lacks cysteine does not allow selective CoWBplating from a CoWB bath stored for more than 12 hours at PdCl₂concentration of 10 ppm or less.

FIG. 25C shows the selective formation of cysteine on the copper patternfollowed by activation with 10 ppm PdCl₂ sensitizer agent followed byCoWB plating according to the method of the present example. In thiscase, a Co peak is observed in the EDX spectra indicating that CoWB didselectively plate onto the sensitizer agent on the copper pattern. Thisis confirmed in the Co map in FIG. 25C. Thus, the method of example 8does allow CoWB plating at PdCl₂ concentration of 10 ppm or less.

FIG. 26 shows that a higher amount of Pd sensitizer agent is required inthe prior art method to selectively plate CoWB than the method of thepresent example. As shown in FIG. 26, CoWB from a stored bath was firstselectively plated onto Cu when 20 to 50 ppm of the PdCl₂ sensitizeragent was provided on copper. The Pd sensitizer agent is provided byplacing a copper substrate in 20 or 50 or 2 ppm of the PdCl₂ sensitizeragent solution such that a Pd⁺⁺ ion selectively reacts with copper andforms Pd on top of the copper surface. The CoWB did not deposit onsilicon which was not sensitized with Pd. However, CoWB did not plateonto Cu or Si when 2 ppm of PdCl₂ sensitizer agent was provided on Cu.The prior art method includes the following steps:

-   -   1. Clean the Cu surface (1 min. in pH 10 NaOH, DI rinse; 1 min.        in 2% H₂SO₄, DI rinse);    -   2. Pd activation (30-45 sec.): 50 ppm or 20 ppm PdCl₂ in 0.5 M        H₂SO₄;    -   3. DI rinse;    -   4. Electroless CoWB plating (1 min.): 0.1 M CoSO₄, 0.3 M        (NH₄)₃C₆H₅O₇, 0.03 M H₂WO₄, 0.06 M DMAB (bath stored for more        than 12 hours);    -   5. DI rinse.

However, the prior art method lacks the cysteine deposition step. Thus,the method of example 8 allows the use of a lower amount of expensive Pdsensitizer agent, such as about 15 ppm or less, for example 5 to 10 ppm,of PdCl₂ to selectively plate CoWB from a bath that is stored more than12 hours.

A different exemplary process for CoP plating according to example 8includes the following steps:

-   -   1. Clean Cu surface (1 min pH 10 NaOH, DI rinse; 1 min in 2%        H₂SO₄, DI rinse);    -   2. Cysteine adsorption (30 s-60 s): 10 mM cysteine in 0.5 M        H₂SO₄;    -   3. DI rinse;    -   4. Pd activation (30-45 s): 5 or 10 ppm PdCl₂ in 0.5 M H₂SO₄;    -   5. DI rinse;    -   6. Plate CoP (1 min): 0.062 M Co(OH)₂, 0.25 M H₃PO₂, 0.5 M        Na₃C₆H₅O₇, 0.4 M H₃BO₃, NH₄OH adjusting pH to 9.2˜9.3, 80 C;    -   7. DI rinse, N₂ drying.

As shown in FIGS. 27A and 27B, only the use of a small organic molecule,such as cysteine, which has a first functionality which selectivelybinds to the patterned copper layer and a second functionality whichbinds to a plating sensitizer agent, resulted in consistent selectiveCoWB (FIG. 27A) and CoP (FIG. 27B) plating under conditions where theabove described prior art method does not achieve selective plating. Forexample, as shown in FIG. 27A, only the copper which was sensitized withcysteine and a low concentration of PdCl₂ sensitizer agent (10 ppm orless) allowed consistent selective CoWB plating. The untreated copperand copper treated with glycine, cysteamine or 2-ATP followed by Pdsensitization did not result in consistent CoWB plating. 4-ATP and3-mercaptopropionic acid also does not appear to allow consistentselective plating of CoWB at low Pd concentration. Thus, only cysteineenabled consistent plating of CoWB under conditions where the prior artprocess does not plate.

Likewise, as shown in FIG. 27B, only the copper which was sensitizedwith cysteine and a low concentration of PdCl₂ sensitizer agent (10 ppmor less) allowed consistent selective CoP plating. The untreated copperand copper treated with glycine, cysteamine or 3-mercaptopropionic aciddoes not appear to allow consistent selective plating of CoP at low Pdconcentration. Thus, only cysteine enabled consistent plating of CoPunder conditions where the prior art process does not plate.

Without wishing to be bound by a particular theory, the presentinventors believe that the thiol moiety of cysteine is important to thisprocess since glycine treatment does not enable CoWB or CoP plating.However, the thiol moiety alone is not sufficient since 2-ATP, 4-ATP,and cysteamine do not appear to plate CoWB and cysteamine does notappear to plate CoP at low Pd concentration. Thus, it is believed thatcysteine's thiol group interacts with the underlying metal layer, suchas Cu, and not the dielectric material to selectively localize cysteinemolecules on the metal layer. Pd ions associate with cysteine's carbonyland/or amine moieties and will initiate CoWB or CoP selective plating.However, since 3-mercaptopropionic acid and cysteamine also do notappear to plate CoWB or CoP at low Pd concentration, it is possible thatPd ions associate with both of cysteine's carbonyl and amine moieties oronly with the non-terminal amine moiety. Of course it is also possiblethat the thiol moiety associates with the Pd ions rather than with theCu surface. In summary, cysteine has three functional groups (thiol,amine, carboxylic acid). It appears that all three-functional groupscontribute to the above described process. However, cysteine can stillbe considered to be a bifunctional molecule having three functionalgroups, two of which may be cooperating to perform one of the twofunctions. The result is that cysteine enables consistent plating ofCoWB and CoP under conditions where the standard process does not plate.Thus, it is the bifunctionality of the small molecule that apparentlyprovides the ability to plate the metal at a lower sensitizer agentconcentration than the prior art. It should be noted that the smallorganic molecule should not be considered to be limited to cysteine.Cysteine was used to show the advantage of bifunctional versus singlefunctional small organic molecules. Other bifunctional molecules may beused for sensitizer agents other than Pd and for underlying metal layersother than Cu.

FIGS. 28A-D illustrate the effect of cysteine and Pd incubation time onthe plating of CoWB. In FIGS. 28A-D, the Pd concentration is 25 ppmPdCl₂ in 0.5 M H₂SO₄, and cysteine concentration is 10 mM in 0.5 MH₂SO₄.

As shown in FIG. 28A, CoWB plated onto a cysteine and Pd sensitizedcopper pattern after a 2 minute cysteine and a 1 minute Pd incubationtime. Likewise, as shown in FIG. 28B, CoWB plated onto a cysteine and Pdsensitized copper pattern after a 1 minute cysteine and a 2 minute Pdincubation time. Likewise, as shown in FIG. 28C, CoWB plated onto acysteine and Pd sensitized copper pattern after a 1 minute cysteine anda 1 minute Pd incubation time.

The upper micrographs in FIGS. 28A-C show the CoWB deposition while thelower EDX spectra show Co peaks consistent with CoWB plating. The uppermicrographs show that the longer Pd incubation time in FIG. 28B resultedin rougher plated CoWB lines. The Cu, Co and Si maps on the right sideof FIG. 28C show that Co is selectively deposited over the Cu lines butnot over Si substrate regions exposed between the Cu lines.

FIG. 28D shows that very short Pd incubation time leads to no selectiveCoWB plating. CoWB did not plate onto a cysteine and Pd sensitizedcopper pattern after a 1 minute cysteine and a 30 second Pd incubationtime because the Co peak is absent in the EDX spectra in the lowerportion of FIG. 28D.

Thus, without wishing to be bound by a particular theory, it is believedthat FIGS. 28A-D show that cysteine incubation time does not appear toaffect small Cu lines, but Pd incubation time has an effect on Co alloyplating. Longer incubation leads to rough Co alloy lines (FIG. 28B) andshorter incubation time results in no plating at all (FIG. 28D).However, the rough Co alloy lines may also be due to “islands” of Pdsensitization that plate spots of CoWB film on the Cu lines.

FIG. 28E illustrates CoP plating on cysteine and Pd sensitized copperlines. Specifically, CoP is plated on 300 nm copper pattern sensitizedwith 1 minute cysteine incubation and 1 minute, 5 ppm PdCl₂ activation.The upper left micrograph in FIG. 28E shows the CoP deposition while thelower EDX spectra shows a Co peak consistent with CoP plating. The Cu,Co and Si maps on the right side of FIG. 28E show that Co is selectivelydeposited over the Cu lines but not over Si substrate regions exposedbetween the Cu lines. FIG. 28F shows a micrograph of a cross sectionalview of a diced Cu pattern. FIG. 28G shows a micrograph of a crosssectional view of the cysteine/Pd sensitized Cu pattern containing aselectively plated CoP cap. The CoP cap is about 100 nm thick and isplated in about 1 minute.

Example 9 Using a Protein Biological Agent to Form a Cap Layer

In example 9, a bifunctional protein biological agent is used inselective deposition of the cap layer over an underlying metal layer.For example, a fusion protein with thioredoxin (“Trx”) as the scaffoldmay be used, as illustrated in FIG. 29. Two variable binding regions maybe added into this scaffold, as shown on the left side of FIG. 29. Thefirst region is a selective binding region for copper and its alloys(CuAl, CuSi, CuAlSi, etc.). The second region is a selective bindingregion for cobalt and its alloys (CoWB, CoWP, CoPt, CoPd, etc.). FIG. 29also shows the use of cell display and phage display libraries todevelop the copper and cobalt binding regions. The right side of FIG. 29shows that the fusion protein is selectively deposited on coppermetallization, such as a copper interconnect or electrode, and the caplayer material is then selectively plated onto the protein with theassistance of a sensitizer agent, such as Co, CoPt or Pd nanoparticles,for example.

The copper binding region may be a binding loop consisting of 14 aminoacids. The variable part is the 12 central amino acids. The sequencesfor this region are shown in the table I below.

TABLE I (SEQ ID NOS: 5-13, respectively, in order of appearance)

The cobalt binding region sequences shown in the table II below can beeither loop or linear sequences and be inserted at the end terminus ofthe fusion protein.

TABLE II SEQ ID NOS: 14-39, respectively, in order of appearance)Sequence SDPKPHSSPYFG FDSEKHPTFRTR YQHPTTAHQLPI IQPNAAHAQAVRSHQTSNYKPIVL NSRHPDYDAVSM SVSVGMKPSPRP NYSAYTPRQALV AAMHQHWQRSLLCTQLSKHQC CPNTKTNHC CHENSPREC CLSVPGRAC CMKSQLTLC CFPHLKGYC CPNHSSSKCCLPITTKTC CTQNKTRDC CKQPMYNTC CTPKNTHTC CNTSMHPLC CGIQGKHRCACNAGDHANCGGGS-amide KLHSSPHTPLVQGGGS-amide HYPTLPLGSSTYGGGS-amideAEPGHDAVP-amide

The first 22 sequences were discovered using phage display techniquesand the last 4 sequences are from prior discoveries or from theliterature. The bifunctional protein may have any combination of thecopper and cobalt binding sites shown in the tables above. Furthermore,scaffolds other than thioredoxin may be used.

FIGS. 30A and 30B show photographs of nine 1 mL eppendorf tubes toillustrate how the bifunctional proteins selectively stabilize cobalt(FIG. 30A) and a cobalt alloy (CoPt, FIG. 30B) nanoparticles. Thesenanoparticles can be used as the seed for selective metal plating, suchas CoWB or CoWP cap layer plating for example. The left most tube inboth Figures contained no bifunctional protein. The other eight tubescontained one of the Trx bifunctional proteins. Each of the eight tubesis labeled X/P10, where the number X represents the clone number of oneof the copper binding sequences in table I above, and P10 represents theHYPTLPLGSSTYGGGS-amide (SEQ ID NO: 38) cobalt binding sequence fromtable II above. Thus, the 7/P10 protein in tube number two representsthe CRDQAGLKVSGAPC-thioredoxin-HYPTLPLGSSTYGGGS-amide bifunctionalprotein (SEQ ID NOS: 5 and 38, respectively).

As shown in the Figures, when the protein is not added to Co and CoPtnanoparticles (tube #1), Co and CoPt nanoparticles precipitate aftercentrifuging at 10,000 rpm for 2 minutes (clear solution is visible inthe lower portion of the Figures). When the X/P10 Trx bifunctionalproteins are added, Co and CoPt nanoparticles remain in the solution(brown color in tubes #2-#9 in the lower portion of the Figures) aftercentrifuging at 10,000 rpm for 2 minutes. Thus, the bifunctionalproteins can stabilize/nucleate Co and Co alloy nanoparticles which canbe used as a seed for subsequent selective cap layer, copper electrodelayer and/or barrier layer plating.

The experimental conditions in FIG. 30A (Co nanoparticles) were asfollows:

-   -   Precursors: 2 mM CoSO₄, 3 mM (NH₄)₃C₆H₅O₇, pH=9.0    -   100 μM Protein: X/P10 Trx bifunctional proteins    -   Reduction: 150 μl of 1 M NaBH₄ added to 500 μl of the above        precursor, 231 mM final concentration of NaBH₄.

The experimental conditions in FIG. 30B (CoPt nanoparticles) were asfollows:

-   -   Precursors: 1 mM Co(acetate)₂, 1 mM K₂PtCl₄, 100 mM HEPES,        pH=7.5    -   100 μM Protein: X/P10 Trx bifunctional proteins    -   Reduction: 10 μl of 1M NaBH₄ added to 500 μl of above        precursors, 20 mM final concentration of NaBH₄.    -   In total, 198 Co—Cu Bifunctional thioredoxin scaffolds were        synthesized as bifunctional proteins to use as seed layer        initiators.

The Cu14/CoPt2 scaffold enables the plating of a Co alloy onto a low-ksubstrate. As shown in FIG. 31A, 5 μL of the CoPd precursor formulation(CoSO₄ (2 mM, 100 μl), K₂PdCl₄ (20 mM, 10 μl), Cu14/CoPt2 (1.4 mM, 4μl), and NaBH₄ (1M, 5 μl) were incubated on a low-k substrate for 5minutes to form the seed layer. The seed layer/substrate was thenexposed to a CoWP plating solution, and a CoWP film was formedsuccessfully as shown in FIG. 31B, which illustrates an SEM image of theCoWP film (top), a side cross sectional view of the CoWP film over thelow-k dielectric on a wafer (middle) and an EDX spectra of the CoWP film(bottom). This film also passed a standard tape test, as shown in thebottom of FIG. 31A.

Example 10 Combining Cysteine Adsorption Step with Acid Cleaning Step

In example 8, a process was described for seed layer deposition andsubsequent plating using a biological molecule, such as the followingprocess:

-   -   1. Clean Cu surface        -   a. 60 s ultrasonic clean, 1:30 dilution ESC-797, DI rinse        -   b. 10 s dip in 2% H₂SO₄, DI rinse.    -   2. Biomolecule adsorption (60 s): incubation with 10 mM        cysteine, 0.5 M H₂SO₄    -   3. DI rinse    -   4. Pd activation (60 s): incubation with 5 ppm PdCl₂, 0.5 M        H₂SO₄    -   5. DI rinse    -   6. Plate CoWP (60 s) in plating bath comprising of 0.062 M        Co(OH)₂, 0.25 M H₃PO₂, 0.5 M Na₃C₆H₅O₇, 0.4 M H₃BO₃, 0.05 M        Na₂WO₄, and NH₄OH adjusting pH to 9.0˜9.5 at 70˜75° C.        If desired, step 1b can be eliminated.

Alternatively, step 1b is eliminated and step 2 is conducted byincubating the substrate for 60 s in 2% H₂SO₄ (instead of 0.5M H₂SO₄)which contains 10 mM cysteine. It has been demonstrated that theaddition of cysteine in the acid cleaning step is beneficial for severalreasons. The cleaning step with added cysteine serves the dual purposeof stripping the copper oxide layer while depositing cysteine on theexposed copper, effectively eliminating a process step. In addition,cysteine acts as an effective corrosion inhibitor during the acidcleaning process, limiting the line resistance increase that would occurwhen using acid alone. The results after the CoWP plating step in thisalternative process are shown in FIG. 32, where film formation occursselectively on the 300 nm Cu lines, not on the low-k spaces.Specifically, FIG. 32 shows the SEM image of the CoWP plating (topleft), the Cu, Co and Si maps (right) and an EDX spectra (bottom).

In general, the seed layer solution preferably comprises cysteine and anacidic solution having a pH of about 7 or less, such that thecomposition enables a selective deposition of a metal ion sensitizer anda subsequent selective plating of a metallic cap layer. The compositionpreferably contains 1 to 100 mM cysteine.

Preferably, the acidic solution having a pH at or less than about 7.0 isa 0.1 to 5 M H₂SO₄ solution. However, other pH 7 or less solutions mayalso be used, such as nitric (HNO₃), hydrochloric (HCl), phosphoric(H₃PO4), sulfuric (H₂SO₄) or acetic acid (CH₃COOH) (or any carboxylicacid derivative) solutions. In general, any chemical species in which aproton is ionized in solution may be used. These acidic solutions may bebuffered or unbuffered. Common buffers used to maintain the pH below 7include (salts or free acids of the following):

-   Maleate (buffers at pH=2.0);-   Phosphate (buffers at pH=2.15);-   Citrate (buffers at pH=3.14);-   Formate (buffers at pH=3.75);-   Succinate (buffers at pH=4.19);-   Benzoate (buffers at pH=4.2) or-   Acetate (buffers at pH=4.76).

Example 11 Bath Composition Variations

As described above, an alkali free CoWP bath may be used to form theCoWP cap layer. One example of the alkali free bath solution is:

0.062 M Co(OH)₂,

0.25 M H₃PO₂,

0.5 M (NH₄)₃C₆H₅O₇,

0.4 M H₃BO₃,

0.03 M H₂WO₄,

NH₄OH adjusting pH to 9.0˜9.5 at 80˜85° C.

Thus, the bath contains NH⁴⁺ instead of Na⁺ ions. One hour plating oncopper surfaces shows a typical composition of Co (91%) W (2%) P (7%)and a good plating selectivity on a 300 nm copper line.

The typical process for preparing a film with this bath is:

-   -   1. Clean Cu surface, cysteine adsorption (10 mM, 30 s-60 s),    -   2. DI rinse,    -   3. Pd activation (10 ppm PdCl₂, 30-60 s),    -   4. DI rinse,    -   5. Plate CoWP (30-60 s),    -   6. DI rinse,    -   7. Dry with N₂ gas.

As seen previously, the cysteine-Pd seed layer selectively bound to 300nm Cu lines on a Cu and low-k patterned substrate, and as a result, theCoWP plated only on the area where the seed layer was deposited. Asshown in FIG. 33 by both SEM (top), mapping (right) and EDX (bottom)spectroscopy, CoWP was not plated on the low-k (Si) lines, but only onthe Cu lines, even after extensive plating times of one hour, with atypical composition of Co (91%) W (2%) P (7%).

The foregoing description of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Thedescription was chosen in order to explain the principles of theinvention and its practical application. It is intended that the scopeof the invention be defined by the claims appended hereto, and theirequivalents.

1. An aqueous CoWP plating bath composition, comprising: a cobalt salt;a reducing agent; a metal chelator; a buffer; and a tungstate salt;wherein a ratio of molar concentrations of the cobalt salt to thereducing agent is from about 1:3 to about 1:5, and a ratio of molarconcentrations of the cobalt salt to the metal chelator is from about1:2.5 to about 1:3.5, wherein at least one of the (i) reducing agent and(ii) metal chelator comprises an alkali metal.
 2. The composition ofclaim 1, wherein the reducing agent comprises a hypophosphite salt. 3.The composition of claim 2, wherein the hypophosphite salt is selectedfrom a group consisting of H₃PO₂, NaH₂PO₂, KH₂PO₂, or NH₄H₂PO₂.
 4. Thecomposition of claim 1, wherein the metal chelator comprises a citratesalt.
 5. The composition of claim 4, wherein the citrate salt isselected from a group consisting of H₃C₆H₅O₇, Na₃C₆H₅O₇, K₃C₆H₅O₇ or(NH₄)₃C₆H₅O₇.
 6. The composition of claim 1, wherein the buffer isselected from a group consisting of H₃BO₃, ethanolamine, TAPS, bicine,or CHES.
 7. The composition of claim 1, wherein: the cobalt salt isselected from a group consisting of CoSO₄, CoCl₂ or Co(OH)₂; thereducing agent comprises a hypophosphite salt selected from a groupconsisting of H₃PO₂, NaH₂PO₂, KH₂PO₂, or NH₄H₂PO₂; the metal chelatorcomprises a citrate salt selected from a group consisting of H₃C₆H₅O₇,Na₃C₆H₅O₇, K₃C₆H₅O₇ or (NH₄)₃C₆H₅O₇; the buffer is selected from a groupconsisting of H₃BO₃, ethanolamine, TAPS, bicine, or CHES; and thetungstate salt is selected from a group consisting of Na₂WO₄, K₂WO₄, or(NH₄)₂ WO₄.
 8. An aqueous CoWP plating bath composition, comprising acobalt salt selected from a group consisting of CoSO₄ or Co(OH)₂; areducing agent comprising a hypophosphite salt selected from a groupconsisting of H₃PO₂ or NH₄H₂PO₂; a metal chelator comprising(NH₄)₃C₆H₅O₇; a buffer selected from a group consisting of H₃BO₃,ethanolamine, TAPS, bicine, or CHES; and a tungstate salt comprising(NH₄)₂WO₄; wherein a ratio of molar concentrations of the cobalt salt tothe reducing agent is from about 1:3 to about 1:5, and a ratio of molarconcentrations of the cobalt salt to the metal chelator is from about1:2.5 to about 1:3.5; wherein the composition comprises cysteine; andwherein the composition comprises an alkali-free bath solution.
 9. Anaqueous CoWP plating bath composition, comprising: from about 0.03 toabout 0.15 M Co(OH)₂; from about 0.05 to about 0.3 M H₃PO₂; from about0.1 to about 0.5 M Na₃C₆H₅O₇; from about 0.3 to about 0.6 M H₃BO₃; andfrom about 0.01 to about 0.08 M Na₂WO₄; wherein the composition has a pHof about 8.0 to about 10.0 at a temperature from about 65 to about 85°C.
 10. An aqueous CoWP plating bath composition, comprising: from about0.03 to about 0.15 M Co(OH)₂ from about 0.05 to about 0.3 M H₃PO₂; fromabout 0.1 to about 0.5 M (NH₄)₃C₆H₅O₇; from about 0.3 to about 0.6 MH₃BO₃; and from about 0.01 to about 0.08 M H₂WO₄ wherein the compositionhas a pH of about 8.0 to about 10.0 at a temperature from about 70 toabout 85° C.; and wherein the composition comprises cysteine.
 11. Thecomposition of claim 1, further comprising cysteine.
 12. The compositionof claim 9, further comprising cysteine.